Move buffer format conversion to its own file and import it.
Make blit_buffer accept memoryviews and objects that implement the buffer interface in additon to bytes. Use new conversion function.
Use proper memoryview for data bufferfmt.
Fix version changed of blit.
Merge branch 'master' of https://github.com/kivy/kivy into memoryview
Merge pull request #2186 from matham/memoryview

Use memoryviews for blit_buffer