fix#773
* buffer_cat is renamed to buffers_cat
* buffer_cat_view is renamed to buffers_cat_view
Actions Required:
* Use buffers_cat instead of buffer_cat
* Use buffers_cat_view instead of buffer_cat_view
fix#773
* buffer_prefix is renamed to buffers_prefix
* buffer_prefix_view is renamed to buffers_prefix_view
Actions Required:
* Use buffers_prefix instead of buffer_prefix
* Use buffers_prefix_view instead of buffer_prefix_view
* Stream write operations now return the number of bytes
transferred from the caller's input buffers.
Actions Required:
* Modify websocket write completion handlers to receive
the extra std::size_t bytes_transferred parameter.
