This class is accessible via the TXN object. It is created only if
the attached proxy have HTTP mode. It contain all the HTTP
manipulation functions:
- req_get_headers
- req_del_header
- req_rep_header
- req_rep_value
- req_add_header
- req_set_header
- req_set_method
- req_set_path
- req_set_query
- req_set_uri
- res_get_headers
- res_del_header
- res_rep_header
- res_rep_value
- res_add_header
- res_set_header