Handle hierarchical module names in External Core tools

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.