I would like to see a broadcast method in the Runtime class. The 
purpose of the broadcast method should be to distribute a public value 
among all parties (or some subset of parties).

A case: All parties in a computation needs to read a value from 
standard in, and it is a different value for each party. We want to 
tell the value to everybody else.

An example use could be like the input method:
a,b,c = runtime.broadcast([1,2,3], value)

Similarly, broadcast can be used in a conditional if only some subset 
of parties wants to distribute a value.