Binding for Anel NET-PwrCtrl devices

A new binding for network-controlled power sockets from Anel-Elektronik.
This rule makes IO1 behave like a push button switch for relay F1. Maybe I should have written that.
I will also add an example rule for a regular switch and add a comment about the push button switch rule. However, one improvement that I made in the meantime is to also catch the unspecified state:
postUpdate(f1, if (f1.state != ON) ON else OFF)