Allow selecting portaudio device by name. - #4732

The only thing I am not sure of is how to properly raise the exception instead of the failwith which gives a badly formatted message.

Looking great!

For the error I would raise a Lang.Invalid_value. It takes the name value (for position) so it's a bit annoying to carry but shouldn't be too hard.

In fact, I would pick the winner earlier on during argument parameters parsing and pass the corresponding value along with a polymorphic variant [Id of int | Name of string] so you can raise an Invalid_value on any error during open regardless of wether id or name was used.

I now raise Error.Invalid_value. This cannot be done during the parsing of arguments because we need portaudio to be initialized when computing the id from the name...