[Enhancement] Communications library for non Apple platforms (#15)

This PR contains the work done to allow the `MakeURLRequestUseCase` use case to be used in non-Apple platforms, as it use has been restricted before.

To provide further details about the work done:
- [x] improved the `MakeURLRequestUseCase` use case to be available in non-Apple platforms;
- [x] moved the `TestEndpoint` helper endpoint to its own file;
- [x] moved some test cases files around;
- [x] updated some text in the `README` file.

Co-authored-by: Javier Cicchelli <javier@rock-n-code.com>
Reviewed-on: #15

Sources/Communications/Use Cases/MakeURLRequestUseCase.swift

@@ -10,9 +10,12 @@
 //
 //===----------------------------------------------------------------------===//
 
-#if os(iOS) || os(macOS) || os(tvOS) || os(watchOS)
 import Foundation
 
+#if canImport(FoundationNetworking)
+import FoundationNetworking
+#endif
+
 /// This use case generate a url request out of a given endpoint.
 public struct MakeURLRequestUseCase {
     
@@ -56,4 +59,3 @@ public struct MakeURLRequestUseCase {
     }
 
 }
-#endif