Defined the Pathable protocol in the library target.

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 type that provides a relative path representation.
+protocol Pathable {
+    
+    // MARK: Properties
+    
+    /// A (relative) path.
+    var path: String { get }
+    
+}