Support overlays

[Tamriel]

Notes created with \pnote[item]<2->{my note} should be visible starting from the second overlay.

[cebe]

as far as I know this is not possible in pdfpc. Slides numbers in pdfpc are per frame and not per overlay so this would be a feature to be requested on pdfpc first before support can be added to this package.

[RyanGibb]

This is now supported in pdfpc: pdfpc/pdfpc#556

[cebe]

Nice, thanks for the hint.