Add statsd-ruby.rb to auto require statsd

By adding lib/statsd-ruby.rb (which just requires statsd.rb), the
'require' option can be omitted when using statsd in a Gemfile.
Merge pull request #43 from lann/master

Add statsd-ruby.rb to auto require statsd
Fix issues with thread local extensions
Bump to 1.2.1
Merge branch 'master' into ipv6_compat