Refactor into workspaces: libcramjam, cramjam-python, and cramjam-cli

[milesgranger]

(Holiday/weekend project)

• Split into workspaces [libcramjam, cramjam-python, cramjam-cli]
• New CLI distribution, first just in python, cramjam-cli exposting all the de/compress core implementations of each variant.

[martindurant]

How did you approach such a thorough rearrangement?

[milesgranger]

Started off trying to implement a CLI interface, became a bit unsatisfied w/ some side-effects of it being inside of Python's library implementation, and anyway had been thinking for a while to make a pure Rust crate, which ought to help with #97. Still a fair amount of shifting things about, like moving the block/frame stuff into libcramjam.

Otherwise, the jist was only to copy the previous cramjam into both libcramjam and cramjam-python then took out things that didn't belong; namely moving <<codec>>::internal::* into libcramjam, and removing from cramjam-python, replacing with libcramjam.