Make use of flask-restful's ReqParser

Per issue #18, added code to look for a "parser" attribute on a method decorated by @swagger.operation.  If parser is found, then it assumes it to be a ReqParser object and extracts overlapping data between ReqParser and Swagger: name, required, description/help and dataType/type.

This requires ReqParser to be defined and added to method as an attribute per this issue comment:
https://github.com/rantav/flask-restful-swagger/issues/18#issuecomment-52113384