Simplify some code

Mostly use instance variables where there used to be templates.
Drop dwgrep.hh, introduce init.hh

- dwgrep.hh contained unfinished old C++ external interfaces that were
  now fully replaced by the C ones.  It also used to contain a couple
  more things, like Dwarf handle and maybe caches, but that's all gone
  at this point, and most of it can be dropped.  The only remaining
  relevant piece is the prototype of dwgrep_vocabulary_core, and that
  should be in init.hh, as it's implemented in init.cc.
Consistent naming in libzwerg/CMakeLists
Change the way doneness of values (raw/cooked) is represented

- Raw and cooked values are considered the same, but have a flag that
  distinguishes one from the other.  The operator words know to check
  this flag to determine what the behavior should be.  This actually
  simplifies code considerably.

- A couple tests need to be turned off.  A replacement is arriving
  shortly.
Plug in gtest

- And rewrite the removed tests in C++.
Update .gitignore