Offset loops

[ThrudPrimrose]

Mainly designed to replace (int i = 1; i < something; i ++) loops with (int i = 0; i < something; i++) loops and thus get rid of having many memlets that look like i - 1, j - 1 by offseting to map and then adding the negative of the offset to the memlets, getting clearer offsets that are easier to read.

The pass supports both Loop regions and maps. And this:

Becomes this:

(The j is offset is correct, I also normalize the loop using the API of loop regions)