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
A new class `serializer` is introduced to permit incremental
serialization of HTTP messages. Existing free functions are
re-implemented in terms of this new class.
* The BodyReader concept is refined to support a greater variety
of strategies for providing buffers representing the body to
the serialization algorithms.
* Added buffer_body, a new model of Body which allows the caller
to provide a series of owned buffers using their own serialization
loop.
* Added empty_body, a model of Body which is for serialization only,
to represent HTTP messages with no content body.
* Removed overloads of write and async_write which send only
the HTTP header.
* Removed public interfaces for performing low-level chunk encoding.
Vinnie Falco