Please support git-bash (msysgit)

Created by: davux

Git-bash is a very powerful bash, posix-compatible implementation for Windows. Currently autojump doesn't support it, as it assumes that "platform=Windows" means you're using the traditional cmd.exe "shell": .bat scripts, C:\Foo\Bar directories and the like. However git-bash provides "normal" bash concepts: .sh scripting, forward-slash (/) separator, one root directory, etc. It does have some specificities: for example the users' home directories are in /c/users/ (equivalent of C:\Users), but you can still use stuff like $HOME and "~/.autojump".

Autojump support on git-bash would be completely awesome. Please add support for it.