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
* 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