Adding parsed_body parameter to simplify checks

parsed_body attempts to parse the post body if it matches a compatible content type
* content is returned unaltered if it's not a compatible type
* content parses json if content-type type is application/json
* content parse querystring params if content-type is application/x-www-form-urlencoded
* if the value cannot be parsed for any reason, it is unaltered
fixing tests for python3
Merge pull request #88 from toumorokoshi/parsed_post

Adding parsed_body parameter to simplify checks