This algorithm allows a socket-like object to be closed in
a generic context. The customization point enables user-defined
types to define the close algorithm to use with `close_socket`.
The nested function lowest_layer and nested type lowest_layer_type
are removed from all stream layers.
Actions Required:
* Remove lowest_layer and lowest_layer_type from user-defined streams.
* Use the get_lowest_layer free function and the lowest_layer_type trait
as needed.
fix#1279, close#1319
This enables users to improve compilation performance by explicitly
instantiating the stream template in another TU.
Signed-off-by: Damian Jarek <damian.jarek93@gmail.com>
close#1322
async initiating functions must return init.result.get(). Returning the
result of post caused a compilation failure for custom completion tokens.
Signed-off-by: Damian Jarek <damian.jarek93@gmail.com>