The resource handler system is now usable but it doesn't perform anything
useful. Although, this will allows it to be tested for correctness.
Minor fixes to HttpResponse output and renaming of functions.
The class now generates default headers. The ETag and Last-Modified tags
do not represent any actual modification time or resource hash.
The basic functionality of the HTTP responses is tested by the core test
suite. More advanced testing of the whole REST API is still required.
Removed the static `create` functions as only the JSON parsing version
could generated errors and even then the errors were unlikely. By
replacing the static creator function with a normal constructor, the
HttpResponse class can now also be created on the stack making its use
easier.
The HttpParser class was renamed to HttpRequest as it parses and processes
only HTTP requests. A second class that creates a HTTP response needs to
be created to handle the response generation.
Moved some of the HTTP constants and helper functions to a separate
http.hh header.
