pickle support for the GraphiteReporter

This is based on https://github.com/BrightcoveOS/metrics-graphite-pickle but refactored for
metrics 3.
update failures on exception
prefer protected over package private
Merge branch 'master' into graphite-pickle

Conflicts:
	metrics-graphite/pom.xml
	metrics-graphite/src/main/java/com/codahale/metrics/graphite/Graphite.java
New URL for documentation

Since it seems to have moved. metrics.codahale.com now redirects to this github repo (dropwizard/metrics), which puts the user in an infinite loop if they want to find the documentation.
Pickled graphite improvements
Persistent connections to graphite
Merge pull request #640 from recampbell/patch-1

New URL for documentation
Formatting fix
Flush graphite after report, also verify close on stop
Defer resolution of hostname supplied to Graphite

Somewhat difficult with UDP, as I don't want to re-resolve on every
single call to 'send'.
Reformatted
Merge pull request #639 from dropwizard/graphite-pickle

GraphiteReporter improvements
Release version 3.1.0!
The long road to 4.0.0 starts now.