Updated the handling of response status codes

Improved API integrity by blocking the ability to set invalid status codes according to the HTTP spec. This includes any non-numeric codes, or any code that is greater or less than 3 digits in length (100-999 being the accepted range).
Updated unit test for HTTP status codes
Updated doc block comment
Merge pull request #1505 from jameswatts/feature/http-status-codes

Updated the handling of HTTP status codes in the response