Add Ruby 2.1.0 to Travis CI mix.
Move Rubinius dependencies from gemspec to Gemfile.
Add WITH_NOKOGIRI to travis test matrix, optionally depending on it in Gemfile.
Remove nokogiri as development dependency, as it's in the Gemfile and is added conditionally based on travis test matrix.
Update travis config.
Use activesupport ~> 4.1 instead of active_support, which doesn't exist any longer.
Add back some C14N-XL tests for JRuby.
Enable C14NXL tests with RBX and REXML.
Attempt to fix active_support/core_ext loading issue.
Version 1.1.1.
Finish 1.1.1.

* Use activesupport ~> 4.1 instead of active_support, which doesn't exist any longer.
* Improved support for RBX and JRuby.