Optionally omit stats_counts metrics

Adds the 'flush_counts' config. Defaults to true, so existing configs
aren't affected.
Support gathering "top" percentile statistics

Adds support for collecting statistics on top percentiles, instead of
the default bottom percentiles. You specify a top percentile by
using a negative number - so -10 will collect the top 10% of data. It
will emit: mean_top10, lower_top10, and sum_top10.

Using a negative number may seem hacky, but it's convenient and there
is a precedent - referencing an array from the end in some languages
can be done with negative indexes.
Added median calculation to timer_data

Added median calculation to timer_data and associated test cases
Changed test case to ensure sorting

Changed the test data in timers_multiple_times_even so make sure the
metrics are sorted before getting the median value. If the data was not
sorted, the median value would be 300 instead of 250.
refactor stat deletion code, no functional changes
delete all metrics in a folder using a command like: delcounters path.to.parent.*
delete stats via management console: move to lib/, docs, generalize, tests
Merge pull request #277 from dynmeth/master

Added median calculation to timer_data
Merge pull request #200 from zwily/upper_percentiles

Support gathering "top" percentile statistics
Add health status functionality
adding SIGTERM handling
initial proxy P.O.C.
Add hashring as optional dependency
Fix link breakage from initial doc split
don't show Bad Line warning for empty strings
use strict comparison for message length
typo
Merge pull request #285 from pshen/master

typo
Fix typo
Merge pull request #287 from zr40/patch-1

Fix typo