Minor README cleanup
Adding a first pass at a "Contributing" section in the README
Renaming private methods
Minor documentation improvements
Renaming 'buffer_size' argument to more accurate 'sample_frame_count'
Consolidating tests for Format.byte_rate and Format.block_align for DRYness

Also being more exhaustive in testing different format combinations.
Updating test code to use the new preferred style for creating a Format instance