Remove bzip2

Proposed following discussion in issue #84 

Implemented as two separate commits-- the first removes the calls to bzip code, and throws a SAM exception (so that it might be more clear if there are people expecting automatic bzip2 encoding/decoding why their code fails). The second removes all traces of the bzip2-related code. They could of course be squished.

Justification: reduce external code/blob dependencies, keep htsjdk focus on its task