Use BooleanType instead of LogicValue
Merge pull request #33 from venables/beta5-boolean-type

Use BooleanType instead of LogicValue for Beta 5
Support for JSON as string

A JSONValue object can now be created directly from a JSON string,
without having to go through an NSData object.

This is done by providing the external parameter name jsonString to the
initializer - consistency could be improved by having named parameters
for the NSData initializer,  as well, but that would be a breaking change.