Use string#foreign_key to support multi-word model classes

See active_support/core_ext/string/inflections.rb. Allows SObject subclasses like 'ActionItem' to correctly infer a foreign key of 'action_item_id'.
Merge pull request #90 from bradstewart/patch-1

Correctly infer foreign_key from associations with multi-word model classes
Fix syntax error in README
Merge pull request #91 from DanOlson/readme

Fix syntax error in README