Message tag escaping per ircv3-specifications issue 71

Fixes #1

	modified:   lib/POE/Filter/IRCv3.pm
	new file:   t/v32_escape_tags.t
Skip message tag escaping on undef values

	modified:   lib/POE/Filter/IRCv3.pm
Merge branch 'escape-tags'

* escape-tags:
  Skip message tag escaping on undef values
  Message tag escaping per ircv3-specifications issue 71