Add event support

Implements code review feedback from https://github.com/ooyala/go-dogstatsd/pull/2
Good catch! The documentation isn't specific about this, but the [official Ruby implementation](https://github.com/DataDog/dogstatsd-ruby/blob/master/lib/statsd.rb#L244) strongly suggests this should be character length. The code uses string#length, which returns character rather than byte length. I'll open another pull with a fix.