New parser set_option function for controlling independent size limits
on headers and body. By default request and response parsers are set up
with reasonable limits to prevent resource exhaustion attacks.
* Parser adheres strictly to rfc7230
* Increased test coverage
* Headers and body maximum size limit options
A new concept Parser is introduced with routines to read from a stream
into the parser. This solves a problem with the old read interface where
messages must be default constructible and move assignable.
Parser fixes:
* Fix detect invalid reason-phrase octets
* Fix write_eof to set the 'complete' state on success
* Fix consider parse complete if eof received on empty body
WebSocket:
* Increase coverage
The version field is moved into message_v1, all public interfaces
are reworked to identify HTTP/1 wire format operations (suffix "_v1")
versus general HTTP.
