Threat control LWRP

Cf. first commit and README changes:

Add a threat_control LWRP, allowing to whitelist/blacklist IPs on CloudFlare
* Stores last action in a node attribute cache, CF API is only called once per day, or if status changes
* IP attribute defaults to current's node IP address
Parenthesis:
https://github.com/bbatsov/ruby-style-guide#method-parens
http://pathfindersoftware.com/2008/10/elements-of-ruby-style/

Based on Ruby current guidelines, the main case we should not put parenthesis is only when there are no parameters. I also remember seeing somewhere that future versions of Ruby may actually enforce functions parenthesis, but I can't find it anymore...

You're completely right on the `return` though. Besides, I hesitated indeed to use directly `cache_status?` in the provider, but I got confused by what is supposed to go in providers, and what goes in resources... Will change.
:construction: