DocC documentation support (#4)

This PR contains the work done to:
* Documented all the `private`, `internal`, and `public` interfaces on the existing codebase;
* Set the DocC documentation catalog in the project;
* Written the main `Library` article for the DocC documentation catalog;
* Added the documentation tasks in 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>

.env

@@ -0,0 +1,11 @@
+# --- DOCUMENTATION ---
+
+DOCC_CATALOG_PATH=./Catalogs/AmiiboService.docc
+DOCC_GITHUB_OUTPUT=./docs
+DOCC_GITHUB_BASE_PATH=amiibo-service
+DOCC_PREVIEW_URL=http://localhost:8080/documentation/amiiboservice
+DOCC_XCODE_OUTPUT=./${SPM_LIBRARY_TARGET}.doccarchive
+
+# -- SWIFT PACKAGE MANAGER ---
+
+SPM_LIBRARY_TARGET=AmiiboService