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
Minor README additions
Merge pull request #226 from rgs/rgs/doc

Minor README additions
This resolves an issue where a random TCP client goes away before a response
is sent from the server. The resulting exception was not handled, and would
cause node.js to crash.

The log file would show this message as a result:
node.js:201
        throw e; // process.nextTick error, or 'error' event on first tick
              ^
Error: write ECONNRESET
    at errnoException (net.js:642:11)
    at Object.afterWrite [as oncomplete] (net.js:480:18)
Merge pull request #227 from f3ew/master

Stability fix
comment out repeater config (not required to run), change host.com to example.com (see rfc2606) in example config