Add Windows support

This patch adds (native, no cygwin/mingw) support for windows to autojump, using [clink](https://code.google.com/p/clink/) to hook on directory changes. All the main functions have been ported, but completion has not yet been added. Most installation types are not supported, only user installation, though I could add them. Errors are also not logged, though it can probably be added. I was just looking to get a functional base working. 

Not sure if this is something you'd want to merge, but I'm definitely already enjoying having autojump on windows.