The previous implementation meant the temp file paths were treated as
regular expressions, which was vulnerable to problems with backslashes
etc.
See #494.
- Hunk stage/undo/preview no longer saves the buffer.
- Hunk undo no longer makes locations go out of sync.
- Grep can be opted out of (grep output with ansi escapes is number one cause
of issues).
- Replaced g:gitgutter_grep_command with g:gitgutter_grep.
- Always runs git-diff the same way instead of in two possible ways.
- Separated detection of git tracking from diffing.
- Simplified path handling.
- Removed support for xolox shell: Windows taskbar does not flash with async
jobs.
- Removed g:gitgutter_{eager,realtime}.
- Simplified implementation generally.
