added JSON helper class with ::format method (used earlier in JSON render)
application/json response will now be formatted when in DEV env

closes #21
Merge branch '3.3/feature/21-json-format' into 3.3/develop
if no error message provided no response body will be generated on error
switched to native "pretty print" for JSON encoding if php version compatible

references #21
made sure that the response content type header is set to the preferred one
making sure error content type is set correctly
added request_data()
added version number to the Core class
removed unnecessary @category comments
minor coding style tweaks
after f222de2 proved to work this RESTful_HTTP_Exception is obsolete

closes #17
minor whitespace and comments tweaks
Merge branch '3.3/develop' into 3.3/release/v2.0