Allow :auto and :guess as targets

These will use node[:ipaddress] and guess_main_ip respectively.

Also, if node[:circonus][:target] is empty and guess_main_ip isn't available,
then use node[:ipaddress] as the IP.
Merge pull request #16 from mivok/node_ip_fix

Allow :auto and :guess as targets
Allow composite metrics
Update README to include composite metrics
Bullet points as bullet points
Formatting changes for README
Be a bit more specific about composite checks and minimum check time
Merge pull request #18 from wanelo-chef/composite-metrics

Composite metrics
Merge branch 'master' of github.com:circonus-labs/circonus-cookbook