Added another arg modifier ' which is used to indicate args to be
wrapped into a closure.

E.g.

coll.where' \x > 2; map' \x * \x; each' writeln: \x

instead of

coll.where: {\x > 2}; map: {\x * \x}; each: {writeln: \x}

Signed-off-by: Jakob Brandsborg Ehmsen <jakobehmsen.github@gmail.com>