Remove Jamfiles and other unused files that stuck around during previous updates.
Add patches for local changes to the patches directory.
Update readme.txt, it had outdated infromation.
The refactoring didn't leave a single file the same, all filenames and classes have bt prefix, methodnames start with lowercase, a single headerfile can be included, and also a single include path.
Plan is to make use of this Bullet 2.x version in extern/bullet2 within the coming weeks, then extern/bullet can be discarded/ignored/content removed.
