The is_deferred nested type is removed from the BodyReader
requirements.
Performance for sending messages with `file_body` was cut
almost in half with is_deferred as `std::true_type` since
it caused double the number of socket writes. If the
deferred behavior is absolutely necessary, callers can get
the same effect by manually sending the headers first.
Actions Required:
* Callers who need the behavior of is_deferred as `std::true_type`
should manually construct a serializer and serialize the header
first, followed by the body.
fix#404
Parsing and serialization interfaces have been fine tuned and unified.
For parsing these stream operations are defined:
* read
* read_header
* read_some
* async_read
* async_read_header
* async_read_some
For serialization these stream operations are defined:
* write
* write_header
* write_some
* async_write
* async_write_header
* async_write_some
serializer interface is changed to be buffer-only, no streams,
and placed in its own header file.
Operations on serializers are moved to free functions as part
of the HTTP write family of synchronous and asynchronous algorithms.
Vinnie Falco