Various CLI improvements.

* Add writehash command
* Add createlog command
* Add appendlog command
* Improve usage text
* 'info' command now handles file-not-found nicer
Merge pull request #15 from spotify/krka/cli_improvements

Looking good, merging. Just a quick note, I think we should rename the assert() function since it has different semantics than the function with the same name in assert.h (Doesn't need -DDEBUG to be executed at all)