lib-http: response parser: Record input stream offset for the start of the last parsed response.

lib-http: Restructured the header, message, request, and response parsers to have an extensible and consistent API using flags. Extended the test suites with a few cases that test parsing with and without the STRICT flag.

lib-http: Added support for creating CONNECT tunnels through HTTP.

lib-http: Implemented limits on overall HTTP header size, size of individual header fields and the number of fields in the header.

lib-http: Adjusted response and request parsers to accept a request/response object to fill with data, rather than have it return one.

lib-http: Moved struct http_response* to http-response.h Also http-client.h now #includes only http-response.h

lib-http: Added initial HTTP client implementation.