Add path option in csv2midi

[josepdecid]

When converting CSV to MIDI, csv.reader requires a file object. I added the option to pass a file path that can be activated with an extra boolean parameter in order to not break current version behaviour.

[timwedde]

Based on the documentation of csv.reader it should also take lists of strings, not just open file objects.
Since this is beta software anyway, I'm not too concerned with keeping the current method parameters as they are, so instead of adding a new parameter I'd rather make the distinction automatic by checking whether the input is a list or file-like object vs a string, which I'd treat as a path.
I've made a fitting commit in 482b9841b7e0044816479228128c7ddb3dff04ec.