Update Monitoring 201 with StatsD.

Add a new paragraph to graphite (on how to normalize metrics), and a section on
StatsD (installation, concepts, etc.).
Add myself to the list of contributors
Add entry about collectd.
Rewrite a few sentences.
Rewrite documentation for gauges and timers.
I can't write the name of my company correctly.
Small fix.
Replace incorrect use of * with " (was breaking the build)
Fix grammar and spelling errors reported by Mike.
Merge pull request #72 from franckcuny/statsd

Statsd