Fixes code example formatting in the README
Adds specs for disallowing YAML and symbol types
Adds implementation for disallowing YAML and symbol types
Adds more specs cover when YAML and Symbol are specifically allowed
Adds documentation for disallowing types while parsing
Fixes contribution guide and YARD task
Merge pull request #34 from nate/hotfix/remove-ability-to-parse-symbols-and-yaml

Remove ability to parse symbols and yaml