Update homepage URL to point to github.io
`gh-update`: Add UA string to GitHub requests

GitHub API v3 now rejects requests that have no
User-Agent string.

http://developer.github.com/changes/2013-04-24-user-agent-required/
Bump to version 1.2.1
Merge branch 'master' into development

* master:
  Bump to version 1.2.1
  `gh-update`: Add UA string to GitHub requests
  Update homepage URL to point to github.io

Conflicts:
	HISTORY.md
	lib/twig/cli.rb
	twig.gemspec
History: `twig-<subcmd>` -> `twig <subcmd>`