Docs: Reference info added to firewall

Added reference information to the firewall module readme.
Docs: Reference information added to firewall module readme

I have added reference information to the firewall module readme. I also fixed errors introduced during squashing in my last commit.
Docs: code formatting edits on readme

Responding to comments from earlier PR to change formatting for some snippets of puppet code.
Merge pull request #397 from jbondpdx/firewall-readme

Firewall readme
Added support for statistic module
Added unit tests
Update docs, remove feature, and rename property
Merge pull request #400 from hunner/feature/statistic_module_support

Feature/statistic module support
rename stat_prob to stat_probability