Stuff that may make it into future versions (patches welcome!)
 . Add debugging output to stderr from parser if ctx_is_debug()
 . Add thorough documentation of the C++ class
 . Make subclassing affect the template objects created in perl_tags.c
 . Export default tags via XS, so that they can be assigned via register_*
   from Perl (and get rid of alias_*)
 . Turn the linked lists used for contexts, varlists and nclists into some
   type of structure that is more efficient for large numbers of members