php-fpm collector

adds the ability for diamond to collect stats from php-frpm via their
status config like

```pm.status_path = /fpm-status```

Tests are including and passing on my laptop
adding example config in docstrings
needed to add the ?json
only publish valid metrics and not any string values
add in a path value
Update phpfpm.py
Merge pull request #14 from mzupan/add-phpfpm

php-fpm collector