Added stepped ranges

Created by: drosseau

Half of #457 (closed)

Syntax is now: {1..2...7} -> 1 3 5 7 {1..2..7} -> 1 3 5 {a..2...e} -> a c e {a..2..e} -> a c

and similarly for backwards and negatives.

Also added some tests to the examples dir.

(I'm not sure why those two earlier commits are in this.. I let my repo get messed up somehow)