Added IDEA project files to .gitignore
Removed unused variable
Fix `prefixStats` global variable leaking

`prefixStats` is leaked through stats.js and was in global scope of event emitter without failing graphite backend by pure accident.
Now it is read from config.
Removed unused parameter
bumping for v0.7.2 patch release

Let's see if travis will upload a release to npm for us.
Merge pull request #437 from anton-rudeshko/fix-global-leaking

Fix global leaking of prefixStats
fix typo in Gauges section