Optionally omit stats_counts metrics

Adds the 'flush_counts' config. Defaults to true, so existing configs
aren't affected.
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 two addtional graphite backend metrics
Line up concats
remove last_ prefix to avoid admin 'stats' match
add helper script to decide which timers to sample down
description fix
Fixing global leaks
Another global leak
remove orphaned variable
examples: python: added python3 support
examples: python: fixed batch update_stats()

This fixes nasty bug introduced by:
    examples: python: use isinstance() to suport inheritance

Pointy hat to: me
TODO: proper tests for update_stats
examples: python: use .format