1.0.0-b6

* Use SFINAE on return values
* Use beast::error_code instead of nested types
* Tidy up use of GENERATING_DOCS
* Remove obsolete RFC2616 functions
* Add message swap members and free functions
* Add HTTP field value parser containers: ext_list, param_list, token_list
* Fixes for some corner cases in basic_parser_v1
* Configurable limits on headers and body sizes in basic_parser_v1

API Changes:

* ci_equal is moved to beast::http namespace, in rfc7230.hpp

* "DynamicBuffer","dynabuf" renamed from "Streambuf", "streambuf". See:
  http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/n4478.html#requirements.dynamic_buffers

* basic_parser_v1 adheres to rfc7230 as strictly as possible

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