Updated Windows build instructions

[thelusiv]

Well I just got around to posting kcid's file and decided to just make my own and upload it, since I just made some modifications to VDrift today that might as well get included.

While I was at it I got annoyed at having to type the same things over and over in MSYS, so I wrote some scripts to aid the process. Now the entire build environment is set up with one command, and there is now a script to compile Bullet and another to compile VDrift. Hopefully this will streamline the Windows build process a lot.

If you're using Windows and compiling with it please test out these changes and let me know if you have any problems. I have updated the Compiling instructions on the wiki (same link as above) to reflect the new scripts.