Common Lisp: Finishing up the unfinished

[lh2]

This finishes up all the unfinished stuff from the first PR. Beyond a couple of small bugfixes here and there the most notable things are:

• {} blocks now use the same function for statement parsing as the toplevel, which fixes let statements in functions and if's
• Added all the tests for the extentions from chapter 6
• Added support for hash literals
• Added a CLI interface
• Added README

[vhladko]

Nice, let’s go :)