Basic support for non-Apple platforms

This release contains the work done to provide basic support of non Apple platforms.

To provide further details about the work done:

• flattened the folder structure, especially now that the idea to filter folders based on platform is being discarded;
• implemented precompiler processors to filter out platform-specific source code;
• updated the Package file to provide basic support for non-Apple platforms;
• added and also improved some targets to the Makefile file to smooth the current development workflows;
• updated the .gitignore file with references to the .vscode folder and the .env file;
• updated the Swift tools version to v5.7.