Don't create errors at negative offsets.

Fixed #66
Only display problem annotations in the hover.

By default, other annotations (like "2 lines added") are also displayed on the
annotation ruler. We rule them out in the template editor.
Ignore more non-git files.
Merge pull request #67 from dragos/issue/unclosed-comment-66

Don't create errors at negative offsets.
Merge pull request #68 from dragos/master

Only display problem annotations in the hover.