Added (first version of) sample Hummingbird app. (#4)

This PR contains the work done to:
* Implemented a basic `Hummingbird` application in which to integrate the `HummingbirdDocC` library.
* Added the *ArgumentParser* package dependency to the `Package.swift` file;
* Added a new *sample* target to the `Package.swift` file;
* Added library and documentation tasks to the `Makefile` file.

Reviewed-on: #4
Co-authored-by: Javier Cicchelli <javier@rock-n-code.com>
Co-committed-by: Javier Cicchelli <javier@rock-n-code.com>

Sources/HummingbirdDocC/Internal/Extensions/LoggerMetadata+Helpers.swift

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+// ===----------------------------------------------------------------------===
+//
+// This source file is part of the Hummingbird DocC Middleware open source project
+//
+// Copyright (c) 2025 Röck+Cöde VoF. and the Hummingbird DocC Middleware project authors
+// Licensed under the EUPL 1.2 or later.
+//
+// See LICENSE for license information
+// See CONTRIBUTORS for the list of Hummingbird DocC Middleware project authors
+//
+// ===----------------------------------------------------------------------===
+
+import protocol Hummingbird.RequestContext
+
+import struct Hummingbird.HTTPResponse
+import struct Hummingbird.Request
+import struct Logging.Logger
+
+extension Logger.Metadata {
+    
+    // MARK: Functions
+    
+    /// Generates a dictionary to use as metadata for events to log into the logging system.
+    /// - Parameters:
+    ///   - context: A type that contains all the parameters associated with a given request, and that conforms to the `RequestContext` protocol.
+    ///   - request: A type that contains all the parameters to process as a request.
+    ///   - statusCode: A representation of a response status to provide as a response.
+    ///   - redirect: A URI path to use in a redirection event, if any.
+    /// - Returns: A generated metadata dictionary for an event to log into the logging system.
+    static func metadata(
+        context: any RequestContext,
+        request: Request,
+        statusCode: HTTPResponse.Status,
+        redirect: String? = nil
+    ) -> Self {
+        var metadata: Logger.Metadata = [
+            "hb.request.id": "\(context.id)",
+            "hb.request.method": "\(request.method.rawValue)",
+            "hb.request.path": "\(request.uri.path)",
+            "hb.request.status": "\(statusCode.code)"
+        ]
+        
+        if let redirect {
+            metadata["hb.request.redirect"] = "\(redirect)"
+        }
+        
+        return metadata
+    }
+    
+}

Sources/HummingbirdDocC/Internal/Extensions/String+Constants.swift

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+// ===----------------------------------------------------------------------===
+//
+// This source file is part of the Hummingbird DocC Middleware open source project
+//
+// Copyright (c) 2025 Röck+Cöde VoF. and the Hummingbird DocC Middleware project authors
+// Licensed under the EUPL 1.2 or later.
+//
+// See LICENSE for license information
+// See CONTRIBUTORS for the list of Hummingbird DocC Middleware project authors
+//
+// ===----------------------------------------------------------------------===
+
+extension String {
+    /// An empty string.
+    static let empty = ""
+    
+    /// A namespace that defines logging values.
+    enum Logging {
+        /// A name of the middleware that triggered a logging event.
+        static let source = "DocCMiddleware"
+    }
+    
+    /// A namespace that defines relative path values.
+    enum Path {
+        /// A forwarding slash.
+        static let forwardSlash = "/"
+        /// An indication of a previous folder in a path component.
+        static let previousFolder = ".."
+    }
+}

Sources/HummingbirdDocC/Internal/Extensions/String+Formats.swift

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+// ===----------------------------------------------------------------------===
+//
+// This source file is part of the Hummingbird DocC Middleware open source project
+//
+// Copyright (c) 2025 Röck+Cöde VoF. and the Hummingbird DocC Middleware project authors
+// Licensed under the EUPL 1.2 or later.
+//
+// See LICENSE for license information
+// See CONTRIBUTORS for the list of Hummingbird DocC Middleware project authors
+//
+// ===----------------------------------------------------------------------===
+
+extension String {
+    /// A namespace that defines the format patterns used to generate strings.
+    enum Format {
+        /// A namespace that defines the format patterns used to generate relative path representations.
+        enum Path {
+            /// A format pattern used to generate relative paths that starts with the `/` string and finishes with the `.doccarchive` string.
+            static let archive = "/%@.doccarchive"
+            /// A format pattern used to generate relative paths that starts with the `/data` string.
+            static let data = "/data/%@"
+            /// A format pattern used to generate relative paths that starts with the `/docs` string.
+            static let docs = "/docs/%@"
+            /// A format pattern used to generate relative paths that finishes with the `/documentation` string.
+            static let documentation = "%@documentation"
+            /// A format pattern used to generate relative paths for JSON documentation files.
+            static let documentationJSON = "/data/documentation/%@.json"
+            /// A format pattern used to generate relative paths that starts and finishes with the `/` string.
+            static let folder = "/%@/"
+            ///A format pattern used to generate relative paths that finishes with the `/` string.
+            static let forwardSlash = "%@/"
+            /// A format pattern used to generate relative paths for index files.
+            static let index = "%@/%@/index.html"
+            /// A format pattern used to generate relative paths that starts with the `/` string.
+            static let root = "/%@"
+        }
+    }
+}

Sources/HummingbirdDocC/Internal/Extensions/String+Helpers.swift

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+// ===----------------------------------------------------------------------===
+//
+// This source file is part of the Hummingbird DocC Middleware open source project
+//
+// Copyright (c) 2025 Röck+Cöde VoF. and the Hummingbird DocC Middleware project authors
+// Licensed under the EUPL 1.2 or later.
+//
+// See LICENSE for license information
+// See CONTRIBUTORS for the list of Hummingbird DocC Middleware project authors
+//
+// ===----------------------------------------------------------------------===
+
+import RegexBuilder
+
+extension String {
+    
+    /// Subtracts a prefix from a string.
+    /// - Parameters:
+    ///   - prefix: A prefix to remove from a string.
+    /// - Returns: A new string with a prefix removed, if any.
+    func subtract(
+        _ prefix: String
+    ) -> String? {
+        let reference = Reference(String.self)
+        let pattern = Regex {
+            prefix
+            Optionally {
+                Capture(as: reference) {
+                    OneOrMore(.anyNonNewline)
+                } transform: { output in
+                    String(output)
+                }
+            }
+        }
+        
+        guard let matches = self.prefixMatch(of: pattern) else {
+            return nil
+        }
+        guard let subtracted = matches.output.1 else {
+            return .empty
+        }
+
+        return subtracted
+    }
+    
+}