Some nice updates/improvements to sy-git.el

* gitgoodies:
  Drastically improve the speed of #'sy-git-blame
  Make #'sy-git-blame somewhat pretty and useful.
  Improve process handling in sy-git.el.
  Add a minor mode and keybindings to sy-git.
  Update/improve sy-git-log, sy-git-blame.
  Add rudimentary support for git diff, blame, and log.