ctf: BitBuffer improvements

ctf: BitBuffer improvements

Minor performance improvements. Simplified the API a bit:
Removed the 'index' parameter from the public API in read()
and put() methods. All reads/writes can be done from the
current position, and this position can be set with position().

Updated the tests accordingly.

Change-Id: I24b30f2a2e5d79be1b873795ebd4183b70551907
Signed-off-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Signed-off-by: Alexandre Montplaisir <alexmonthy@voxpopuli.im>
Reviewed-on: https://git.eclipse.org/r/7076
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>