fixes to buffered client, adds floats and delta gauges

I started using your statsd package. I found the buffered client didn't support %HOST%, so I fixed that. I found there was a typo in buffered gauges.

Then I realized that gauges needed two APIS, one for absolute valued gauges, and one for deltas. So I split the gauge API into the regular gauge (Gauge() and FGauge()) and deltas (GaugeDelta() and FGaugeDelta()). That let me handle negative gauge values correctly.

You can pick and choose whatever you like (especially since the GaugeDelta() change breaks the API --- the existing API is that a regular Gauge() is delta, while a buffered gauge is absolute for + values, and delta for negative values, which is somewhat broken)

-Nicolas Dade
This went with 'hostname' being truncated to the first part of the FQDN.

The IT guy who runs the dashboard didn't want the full hostname being part of the stat name. So I first truncated, then simply made Hostname external so the calling code could simply alter it to suit themselves.

I think in the end exporting Hostname is the right solution, and let the calling code edit it as they desire if the default FQDN isn't right.