v1.4.0

• FEAT: Adds ParserConfig, a new type to allow making some parsing rules more or less strict, or otherwise customize the parsing.
• FEAT: Adds ParserConfig::allow_spaces_after_header_name_in_responses(bool), which when set to true, will allow skipping spaces between a header name and the colon. The specification requires that to be illegal in most cases, but says proxies should accept and remove those spaces.