Add parser for MeCard format

This was originally used for a more compact vCard representation, but today
is mostly relevant for Wifi configuration QR codes.

See https://en.wikipedia.org/wiki/MeCard_(QR_code)
and https://github.com/zxing/zxing/wiki/Barcode-Contents#wi-fi-network-config-android-ios-11

Lifted from QRCA for use in other places, such as plasma-nm.