Allows booleans and enumerated fields to work with yard-rest-plugin

The yard-rest-plugin has been documented to display it's "types" as
camel-cased strings, and that is same string value that is used when
generating docs in IODocs.  Unfortunately the template uses lowercase
strings from it's comparison to do this, so the boolean and enumerated
value types will never work.

Since it is easier to coerce the strings to lowercase then it is to
force a standard on to other API's generating documentation specs, this
was a obvious choice.