Bugfix/help text and reorder rename args

[bmcdonnell]

c0b4b96 and d6e43fd add/revise some help text. I think it's a given that you'll want to pull those in, except maybe if you want to change the printout order or something.

cf3885e may be debatable. It flips the order of the rename sub-subcommand arguments to match git conventions--most compellingly, git branch --move [<oldbranch>] <newbranch> (where oldbranch is optional and first). In other cases, "old" isn't optional, but it's still first:

• git mv <source> <destination>
• git diff <oldcommit> [<newcommit>]
• git remote rename <old> <new>

Since rename was just introduced in 1.11.0, less than a year ago, it wasn't fully documented, and error messages should point users in the right direction, would you consider this change is a reasonably small disruption?

[ChrisJStone]

I'm in the process of updating gitflow. If you could kindly resubmit your pull request against my fork here as it appears this fork is no longer being updated.