Removes string parameter validation and number coercion

This is in response to #111 - I just can't see any reason why the parser should assume that a parameter declared as a string and passed in as a string should try to convert it to a number and throw an error if it succeeds. 

Figured I'd go ahead and remove it so that, if you agree with #111, there's no additional work to do. (Though I'd appreciate a version bump when/if this is merged)