Return the metric instance for every StatsD call.

The should always be a truish value. The only exception is when calling StastD.measure with a block, in which case it will return the return value of the block.
Merge pull request #41 from Shopify/return_metric

Return the metric instance for every StatsD call.
Bump version
Use CLOCK_MONOTONIC instead of Time.now

CLOCK_REALTIME is affected by leap seconds and NTP adjustments making it less than ideal for measuring intervals.