Optionally omit stats_counts metrics

Adds the 'flush_counts' config. Defaults to true, so existing configs
aren't affected.
    add config (deleteIdleStats) to delete idle sets, gauges, timers - and a overall flag to set them all but allow individual overrides
    update delete_counters unit test to test deleteIdleStats which covers all stat types
update readme and example for deleteIdleStats and friends
reorder example for easier merge
reorder example for easier merge
Remove extra Object.keys check in the timer_data loop
Merge pull request #255 from etsy/optimize-graphiteBackend

Remove extra Object.keys check in the timer_data loop
Add support for gauge deltas.

* Add tests for gauges and new gauge deltas.
* Add support for +/- prefix for gauge values to support modifying
  gauge values in-place.
Remove numStats asserts.
Merge pull request #72 from jsocol/modify-gauge

Add support for gauge deltas.
Update readme with gauge delta info.
Merge pull request #256 from jsocol/gauge-readme

Update readme with gauge delta info.
remove duplicate code, and fix global leak
pulled out the wrong set
Merge pull request #257 from etsy/optimize-graphiteBackend-more

remove duplicate code, and fix global leak
Just join once.
OCD
Logging is for debug mode
Merge pull request #258 from etsy/optimizations

More graphite backend Optimizations
only split the packet if we need to