This function converts integers to their decimal
representation as a static string.
In addition, static_string::resize no longer initializes
characters if the new size is larger.
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