Point to the new repo for ruby-gumbo

[Changed owners](https://github.com/galdor/ruby-gumbo/commit/b2b4cc22e66a19b677098c0692dcaf38eafe0b7c)
Merge pull request #265 from nevir/patch-1

Point to the new repo for ruby-gumbo
Fix Geoffrey's last name in the THANKS file.
Add Perl bindings to Readme.  Fixes #268.
Merge upstream.
Merge pull request #272 from nostrademons/housekeeping

Housekeeping
Merge remote-tracking branch 'upstream/master' into template_tag
Merge branch 'master' of https://github.com/google/gumbo-parser into template_tag
Add GUMBO_NODE_TEMPLATE and use it throughout the code.  Also fix a bug in popping templates that was caused by the code not being namespace-aware, and write a test case for this.
Fix a couple assertion failures due to existing insertion modes not realizing that GUMBO_TAG_TEMPLATE was now a legal current node.  html5lib_adapter_tests run now, though some fail.
Revamp adoption agency algorithm to match the spec, in particular inserting the moved node to the appropriate place for inserting a node instead of appending it to the current node.
Update Python bindings to be template-aware, and update the html5lib tests accordingly.