O(n) Yield the argument, but force it not to retain any extra
memory, by copying it.
This is especially useful when dealing with slices. For example:
force (slice 0 2 <huge vector>)
Here, the slice retains a reference to the huge vector. Forcing it
creates a copy of just the elements that belong to the slice and
allows the huge vector to be garbage collected.
This function, or withStderrLogging, must be wrapped around
whatever region of your application intends to use logging. Typically
it would be wrapped around the body of main.