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>