This situation has improved a lot within the last year. I'd highly recommend trying out a combination of a-Shell (includes vim!), and WorkingCopy for git. Both of these can access any folder in Files or any external file provider (even outside of their sandbox). SecureShellFish is also great if you want to interface with a server.
And before anyone asks what ViMobile is... I wouldn't know, developing applications for iOS is stupidly hard.
I'd be pretty happy with something like ViMobile, and `git push` personally.