RequestHandler: Extract check of whether a response body is allowed
RequestHandler: Don't throw if chunk/json/form bodies are returned but no body is allowed

This is more annoying than useful. Still, throw if a stream is returned since simply discarding those could leave them hanging.
RequestHandler: Emit event if a response body is ignored
RequestHandler: _assertResponse() should check if response is an object
RequestHandler: Support 'html' values in response object

Either a string or an array, which is assumed to contain a mix of
strings and buffers
Merge pull request #5 from novemberborn/request-handler-improvements

RequestHandler improvements