Ternary Expressions, Improved Integer Divisions, and Iteration Space Fix

Ternary expressions

This MR introduces ast nodes, typification, constant folding, and printing of ternary a ? b : c expressions. On top of that, freezing support for sympy.Piecewise is introduced.

Integer Division Improvements

This MR introduces the PsRem expression node for the C % operator, and adds constant folding for C-style integer division and remainder operations.

Fix: Iteration Space work items

Using the above, this MR fixes the computation of the amount of work items in an interation space if start, stop and step don't align.