Add Config method to rules.Interface
Read and apply conf file to rules
Change the Config method to return an error

This gives rules an opportunity to return an error if configuration
fails and the user needs to be informed.
Ensure that a nil map never gets passed to a rule

This follows the documented behavior in the rules package that states a
conf map will never be nil.
Fix bug when error checking after opening conf

The readConf function's error checking logic was backwards. It now
correctly parses the conf file if there was NOT an error opening the
file.
Merge branch 'conf'

Closes #2.