Add gemspec and license

bundler can't install from git source without gemspec
Support IETF language tags

* recognise subdomains like "en-us", "pt-br" etc
* allow to create custom mappings, e.g. "us" instead of
  "en-us"
Code highlighting in Readme
Acceptance test
Add releasing tasks to Rakefile
Add functional test
Leave only functional test
Move important definition, require "subdomain_locale/railtie" should work fine
Remove "controller test" also
Avoid using global state in unit test
Clean up config
Remove obsolete dependency
Remove Gemfile, it is never used
I18n stub is no longer needed, mapping is used instead
Subdomain-locale mapping can now be customized.