Patched (temporarily) the DocC documentation (#8)

This PR contains the work done to:
* Documented the public properties, initializers, and/or functions of those types conforming to the `APIClient`, `KeyNameFilter`, and `KeyNameModel` protocols, to fix the issue that the protocol documentations cannot be inherited;
* Moved the `AmiiboService` DocC documentation catalog inside the library target;
* Amended the folder structure of the library and test targets;
* Fixed further documentation issues encountered while revising the written documentation;
* Added the `lib-test` task in the `Makefile` file;
* Improved the naming for the existing tasks in the `Makefile` file.

Reviewed-on: #8
Co-authored-by: Javier Cicchelli <javier@rock-n-code.com>
Co-committed-by: Javier Cicchelli <javier@rock-n-code.com>

Package.swift

@@ -42,7 +42,7 @@ let package = Package(
                 .product(name: "OpenAPIRuntime", package: "swift-openapi-runtime"),
                 .product(name: "OpenAPIURLSession", package: "swift-openapi-urlsession")
             ],
-            path: "Sources",
+            path: "Sources/AmiiboService",
             plugins: [
                 .plugin(name: "OpenAPIGenerator", package: "swift-openapi-generator"),
             ]
@@ -52,7 +52,7 @@ let package = Package(
             dependencies: [
                 .byName(name: AmiiboService.target)
             ],
-            path: "Tests"
+            path: "Tests/AmiiboService"
         ),
     ]
 )