* clean git support for ver < 2.0
* fine tune tests for markup (which requires git module)
* remove unnecessary comments
* try to fix tests
* try test again
* use const for GitVersionRequired instead of var
* try to fix integration test
* Refactor CheckAttributeReader to make a *git.Repository version
* update document for commit signing with Gitea's internal gitconfig
* update document for commit signing with Gitea's internal gitconfig
Co-authored-by: Andrew Thornton <art27@cantab.net>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
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