Allow any opcode or function to "wait"

[hvacengi]

@Dunbaratu and I discussed a method to allow any opcode to easily initiate a wait condition while providing logic to check the wait status. This will allow us to have a little more flexibility with features in the future. The most pressing example where we would like to use it is for copying files using remote tech and signal delay.

The logic essentially works out to adding a "yield" method on the Opcode base class, along with a property to determine if the opcode is currently yielding and a method for "checking" the yield condition. The SafeFunctionBase class then also gets a yield method to give functions easy access to the yield feature. In both cases, the yield method would accept a delegate with the logic for determining when to finish yielding.

I already have an implementation of this logic, and will be issuing a PR soon.