Simple syntax for procedures vs. functions

[rnpandya]

A large fraction of my CoffeeScript functions don't return a value, and I frequently find myself adding "return" to avoid generating the code to construct a return value (e.g. if the last statement is a loop). It would be convenient, and would add useful documentation, if there were a very easy way to specify that a function did not return a value, e.g. using "-->" or "==>" instead of "->" and "=>".

[jashkenas]

This is a duplicate of several previous issues.

[TrevorBurnham]

Notably #899.