Feature request: add the ability to ignore blank lines for git blames.

[s4my]

When the cursor is on a blank line, I don't think we should show the git blame, it's mostly useless and annoying. The only use case I can think of, is if you're looking for "who's the idiot who added a blank line here".

So I propose we either add an option in current_line_blame_opts to ignore blank lines, something like ignore_blank_lines: boolean, or ignore blank lines by default all together. This will have an additional performance benifit.

I can work on this, but I don't know what approach you would like me to implement?