#90 Find-all operator

[Martin Büttner]

Simple:

[3 0 1 2 1 0 3 3 0 2 3 3 1 2 2 2 2 1 0 2] 1 ef
--> [2 4 12 17]

It would also be nice if this worked with multi-dimensional arrays, but I think that should probably be part of a larger change, which also allows for multi-dimensional =, t, /, %, ew etc.

[Sp3000]

Would also be good if this took a block, like #

[Sp3000]

Equally useful might be a get-indicies-of-truthy-elements operator, such that the above could be implemented as f=x (assuming x is said operator).