[Ctags] [patch] Add'l Perl support for ctags

[Dmitri T. <dm...@ne...>]

Attached patch is against ctags version 5.5.2.

New feature support in perl parser:

  - support for 'use constant ABC => "xyz";' construct (ABC
    tag is created);
  - support for label constructs:
      EXIT:
    will produce a tag for EXIT;
  - support for full (package name + name) tags for constants
    and subroutines:
      package ABC::XYZ;
      sub hello {         # will create tags 'ABC::XYZ::hello'
                          # and 'hello', in case hello is
                          # called in the first way.
      }


  - Dmitri.