- Added GitSigns*Inline and GitSigns*LnInline to be used with word diff
- GitSigns*LnInline is used for word diff with config.word_diff
- GitSigns*Inline is used for word diff in hunk previews
- Added GitSigns*VirtLn and GitSigns*VirtLnInline to be used with
`config.show_deleted`.
- Define GitSigns highlights conditionally as opposed to only defining
them if certain features are enabled.
Some git command likes `git checkout -b` do no update .git/index.
Instead watch the git dir itself to capture all git operations.
Renamed config.watch_index -> config.watch_gitdir
Fixes#377