Merge branch 'sb/blame-color'

Merge branch 'sb/blame-color'

"git blame" learns to unhighlight uninteresting metadata from the
originating commit on lines that are the same as the previous one,
and also paint lines in different colors depending on the age of
the commit.

* sb/blame-color:
  builtin/blame: add new coloring scheme config
  builtin/blame: highlight recently changed lines
  builtin/blame: dim uninteresting metadata lines