support histograms

in accordance with existing codebase, implement this in graphite
backend
clarify bins can be arbitrarily wide
support different histogram settings for different metrics
bugfix: allow bin upper limits to contain decimals

also modify an example to demonstrate
clarify histogram/bin categorisation algorithm
merge branch 'master'
add tests for histograms
put all histogram bins in a "histogram" sub-hierarchy
add helper script to decide which timers to sample down
description fix
add a bit more debug output - sets, numStats
remove metric name sanitisation. this is a task for the backends
Merge branch 'etsymaster' into p/debugupdates
update debug log to new logger, make all debug prints use consistent DEBUG: prefix by removing the extra arg
bugfix: make sure histogram metric path is correct

also slight optimisation in the metric setting loop for timers
Merge branch 'histogram' of github.com:Dieterbe/statsd into histogram-integration

Conflicts:
	backends/graphite.js
	exampleConfig.js
make histograms work with the graphite backend
Merge pull request #233 from keen99/p/debugupdates

add a bit more debug output - sets, numStats
move percentThreshold in global namespace for now
implement graphite test for histograms