lib-http: message parsers: Record beginning of parsed data.

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: message parser: Don't allocate a pool for the next message until it is needed. This prevents wasting memory when no message is being parsed.

global: unsigned int:1 -> bool:1 perl -i -pe 's/unsigned int ([^,:;]+):1;/bool $1:1;/' **/*.[ch]

lib-http: Added option to the header parser to make it lenient towards illegal characters in header field content. The offending characters are then skipped without error. This is required for the http client as a workaround for bugs in certain HTTP servers. This behavior is explicitly not enabled for the http-request-parser as used by our own HTTP server implementation.

lib-http: Added support for enforcing a payload limit for incoming HTTP messages.

lib-http: Adjusted message and request parsers to return an error code.

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

lib-http: Unified http-request.h and http-response.h headers. Renamed struct http_response_header to struct http_header_field, encapsulated the array in struct http_header and put it all in http-header.h/c Added inline utility functions for header querying and getting response/request payload size.

lib-http: Improved message header and body parsing for better RFC compliance. Added pre-parsed transfer-encoding and connection header content (array) to parsed message struct. Fixed message body handling for when both transfer-encoding and content-length headers are missing. Now duplicates of unique important message headers yield an error.

lib-http: Adjusted message parser to accept pool from caller.

lib-http: Implemented http-request-parser for HTTP servers. Moved code common with it and http-response-parser to http-message-parser.