Split oversized UDP packets containing multiple metrics

This pull request adds a fix for [issue #25](https://github.com/goncalopereira/statsd-csharp-client/issues/25) by attempting to split oversized UDP packets that contains multiple metrics. 

A conservative size of 512 bytes is used as the limit for a UDP packet. See http://stackoverflow.com/questions/1098897/what-is-the-largest-safe-udp-packet-size-on-the-internet for why this number was chosen. It's worth noting that 512 is a relatively conservative limit - theoretical limits are much higher.

Metrics are split in StatsUDP across newlines.