** Don't fear the files-changed list, almost all changes are in the **

** Don't fear the files-changed list, almost all changes are in the **
** file-level documentation at the top of the sources.              **

This is the "make bugzilla stop bugging me" bugfix commit.

* Remove BackedNodeBuilder<> and collapse NodeBuilder<> hierarchy.
  Updated documentation in the file.  Resolves bug #99.

* Convenience NodeBuilders (PlusNodeBuilder, OrNodeBuilder, etc.)
  moved into a separate file.  Partially resolves bug #100.

* Moved isAssociative(Kind) into kind.h (and into the CVC4::kind
  namespace) instead of metakind.h (where it was in CVC4::metakind).
  This clears up a warning (private #inclusion) from the SMT and SMT2
  parsers, and maybe makes more sense anyways, since this is based on
  the kind (and not the metakind) of an operator.

* Documentation improvement; doxygen top-level \file gestures, \brief
  gestures for files, etc.  Changed contrib/update-copyright.pl for
  this change, and post-processed to add \brief.  Resolves bug #98.

* Removed ExprManager::mkExpr(Kind) and NodeManager::mkNode(Kind).
  They no longer made sense.  Resolves bug #91.