[FEATURE] Release 2.1 tracker

[jgabaut]

For amboso 2.1.0, only some basic global config file support is expected.

• [FEATURE] Add support for a global config file #109
  Next release cycle may try to implement these features, but the primary reference implementation will still be invil.

These issues hold some proposed extensions for the 2.1.x API:

• [FEATURE] Add support for more project types #110
• [FEATURE] Replace current toml parsing module with a proper utility #111
• [FEATURE] Rename config file to stego.toml #112
• [FEATURE] Revert thin amboso change from 1.9 #114
• [FEATURE] Collect extension selectors by minor version #115
• [FEATURE] Add collective definition of error codes instead of using inline constants #117