`pick` syntax not fully implemented

[sohpeach]

The ref at http://www.byond.com/docs/ref/#/proc/pick shows pick being used in the following way:

pick (
    "[usr] eats \a [src].",
  prob(50)
    "[usr] devours \a [src].",
  prob(25)
   "[usr] wolfs down \a [src]."
)

Instead of using semicolons to separate the weight from the result, it uses a new-line. The indentation doesn't matter at all.

At the moment all information on whitespace is removed when the indentation pass happens, so this isn't a trivial fix.

I'd ignore this if the syntax was trash, but it looks alright and I can imagine people using it.