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
Core:
* Test buffer_cat iterator move members
HTTP:
* Fixed yield / resume in writer
* Fixed message serialization with chunked encoding
* Test yield / resume in writer
* Test all conditional branches during message serialization
* Test chunked encoding
* Increase coverage on parse_error
* Add parse_error::general
WebSocket:
* Add error::general
* Increase coverage in error
