Added --json option to cc

I'm using the output of this excellent tool for a project, and I needed to import the data that it outputs.

I added an option to get json output on the cc command. I've moved some of the logic outside of radon.cli.cc, but to do it properly all the logic should be moved away from cli. This is not a complete refactor, but it's the smallest change I could made that would provide json output and still be on the good direction.

I've added an analyze_cc function that returns the data in Python objects (so that radon can just be imported by other projects instead of parsing its output).