Implemented the DocC archives support for the middleware (#2)

This PR contains the work done to implement the support for `DocC` archives (or `.doccarchive` containers) into the middleware.

Reviewed-on: rock-n-code/hummingbird-docc-middleware#2
Co-authored-by: Javier Cicchelli <javier@rock-n-code.com>
Co-committed-by: Javier Cicchelli <javier@rock-n-code.com>

Sources/DocCMiddleware/Internal/Protocols/Pathable.swift

@@ -0,0 +1,21 @@
+// ===----------------------------------------------------------------------===
+//
+// 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
+//
+// ===----------------------------------------------------------------------===
+
+/// A protocol that provides a relative path representation.
+protocol Pathable {
+    
+    // MARK: Properties
+    
+    /// A (relative) path to a resource.
+    var path: String { get }
+    
+}