Parameters should better be captured.  This removes some complexity
from Async().

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1102

Stop early, don't try more formats if it is clear that we have no
chance.

Fixes assertion failure in the Thread destructor.

Fixes crash due to std::stoul() throwing std::invalid_argument.

Reduce header dependencies.

Reduce header dependencies.

Reduce header dependencies.

Fixes linker failure on test/run_output.exe

Casting to std::runtime_error loses information (and prevents RVO).

Shorter.
Signed-off-by: Rosen Penev <rosenp@gmail.com>

* Use PcmExport for 24bit packed output