Create arbitrary bit field extraction

Implement parser code that can handle any arbitrary alignment, arbitrary length bit pattern in either Big Endian or Little Endian format and return a BigInt for later trimming and sign-extending by a higher-level Primitives routine.

DFDL-12-150R
DFDL-12-151R
DFDL-12-152R
DFDL-12-153R
DFDL-12-154R
DFDL-12-155R