* Add handler_ptr test and increase coverage
* Add test for prepare_buffer
* Move is_call_possible tests to a .cpp file
* Tidy up docs and declarations
message_headers is now a set of partial class template
specializations instead of a template class alias. This solves
a problem where template functions taking message_headers as a
parameter could not deduce argument types, since std::conditional
obscured the deduced context.
Both classes are refactored to share declarations using an #ifdef,
to eliminate an ugly set of extra declarations needed when building
the documentation.
Copy and move class special members are added.
A new function message::base() is provided which returns the
message_headers portion of a message.
Conform to the Networking TS by renaming the Streambuf concept
to DynamicBuffer in all places. Values of types meeting the
requirements of DynamicBuffer are renamed to dynabuf.
See:
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/n4478.html#requirements.dynamic_buffers
* Headers renamed
* Formal parameter names renamed
* Template argument types renamed
* Documentation updated
