Try to support `Universal Ctags' (issue #123)

Refer to issue 123 on GitHub for details:
  #123

Improve documentation of `easytags_dynamic_files' option

See also issue 92 and issue 116 on GitHub:
 - #92
 - #116

Merge pull request #111: Give precedence to dynamic files over storag…

…e by filetype

I rewrote quite a bit of code in this pull request but I didn't change
the behavior introduced by @cornerman (at least it was not my intention
to do so). The main reason for rewriting was that the name
xolox#easytags#get_global_tagsfile() "was a lie" because it could
select either a file type specific tags files or the global tags file. I
like functions whose name captures what they do so had to change things
around in order to merge pull request 111 without having that name
bother me :-).

See also pull request 111 on GitHub:
  #111

Which came forth from issue 102:
  #102

Improve handling & docs of g:easytags_opts option (issue #98)

Add g:easytags_opts option (issue #98)

See also issue #98 on GitHub:
  #98

Improve Perl function tag highlighting (more accurate now)

As suggested in issue #97, for details see:
  #97

Bug fix for xolox#easytags#filetypes#find_ctags_aliases()

When a canonical Vim file type mapped to a group of file types,
the group was returned without the canonical file type :-s

See also issue #91 on GitHub:
  #91

Change file type canonicalization to treat C as C++

Please refer to the inline comments for more details.
This will hopefully fix issue #91 on GitHub:

  #91

PS. I've completely removed the objc/objcpp grouping because I don't know
    these languages so I don't know what grouping would be correct anyway.
    Until a user with an informed opinion chimes in it's better to just
    remove this grouping.

Support for Perl highlighting (thanks to Jessica Kathleen McIntosh, s…

…ee issue #97)

See issue #97 on GitHub:
  #97

Merge pull request #95: Add g:easytags_suppress_report option