correct parsing of linguist output

thanks @raefko

Quality and Github Actions

• apply black code style
• move CI to GitHub Actions
• improve docs

avoid exe clash

invoke github-linguist to avoid QT Linguist clash

Better accuracy

Script is more careful about detecting important changes that can unduly skew Linguist results, such as:

• changed .gitattributes
• added or untracked files

Reject directories with added, uncommited files

To help avoid mistakes, skip output on directories where files were added locally but not committed, since Linguist doesn't operate on them. This could happen if setting up a new repo.
Yes there are further cases such as unmerged added files from remote, if those cases become an issue let us know.

output simple string option, handle non-Git directories

v0.9.1

handle non-Git directories

Initial release

v0.9.0

release