Start extracting a Language class out of RepoComplexity
Move the loading of the auth.yml file to the Config class
Use GitHub's file extensions index to better detect "interesting" blobs
Slightly improve tests for the RepoComplexity module
Return a repo's colour, as determined by its main language

Introduce a LanguageLibrary class to move responsibility out of the
Language and LanguageDetector classes.
Remove "searchable" field from GitHub's languages.yml file