Sanitize ascii control characters (they're not allowed on Windows)
Sanitize ascii control characters (they're not allowed on Windows)

Fix #147.

Unlike Linux, Windows doesn't allow ASCII control
characters (codepoint < 32) in filenames.  See:

https://stackoverflow.com/a/31976060/6598435

https://docs.microsoft.com/en-us/windows/win32/fileio/naming-a-file#naming-conventions

For consistency, we should remove them always.

This might be a moot issue, since in recent versions of Anki (2.1.43
tested) it seems that all such control characters (including \n) are
already filtered out from deck names, but I don't think it hurts.

\n will be double-counted, but I think it's best to keep it explicitly
for readability (and since we're using a set, duplication doesn't
matter).

The `join` takes just 5 μs, so I think replacing it with the
"computed" string is not worth the drop in readability.

Stvad/CrowdAnki,Stvad/CrowdAnki,Stvad/CrowdAnki