Handle hierarchical module names in External Core tools
I updated the parser to handle hierarchical module names (with package names) the way GHC is currently printing them out in External Core. Beware kludgy use of z-encoding and gratutious copy-pasta from GHC. You can now use the stand-alone Core parser to parse a very simple GHC-generated .hcr file (progress!) but not to typecheck or interpret it (the typechecker/interpreter don't snarf in the right libraries yet, among other things.) And, the parser is still incomplete in that it doesn't handle programs with newtypes/GADTs/etc. whose syntax has changed since 2003. In other words: probably don't try to use this yet.