Fixing CopyRegion and creating faster APIstic ways to handle fast bitmaps

* CopyRegion now uses 'memcpy' and copies whole blocks of memory more precisely
* Added a FastBitmapLocker IDisposable struct that unlocks on dispose
* Now the FastBitmap is a disposable that unlocks on Dispose
* Created static method Bitmap.FastLock() that creates and returns a locked FastBitmap that is ready to be used