Made side_effects test less broken and more interesting.
Made side_effects test less broken and more interesting.

Now it demos complex numbers, and a poor man's version of external consumers.


Former-commit-id: 766634dec5cdbe1c40810a5625156e3ea3115c78
Trass3r/Halide,Trass3r/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,darkbuck/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide