Update linter.rb

pull in and combine multiple .foodcritic files:
the original location in each cookbook, ~/.foodcritic , ~/.chef/.foodcritic

This allows for global settings - ex: I don't agree with FC###, and don't want to check for it EVER.  add "~FC###" to ~/.chef/.foodcritic and Done!
Update linter.rb

Added another common location <chef-repo>/config/.foodcritic

essentially "<cookbook path>/../../config/.foodcritic"  This is useful making a common file as part of your repo to share.
Merge branch 'multi_config_files' of github.com:chazzly/foodcritic into multi_config_files