Implement infix:<x> and infix:<xx> in examples/

[masak]

One as a sub, the other as a macro.

I just went and removed these two operators from core 007 on the master branch. Outside of the tests, the documentation, and the self-hosting, we didn't mention these operators at all. Notably, there was not a single use of them in examples/.

But they're highly user-definable, and nothing is lost by defining them this way. In fact, the kind of provide a cute contrast between when you'd use a sub and when you'd use a macro.

(Why is infix:<xx> a macro? Because we want the "thunkish" behavior of for example. my i = 0; my array = i++ xx 3; (assuming postfix:<++> for convenience) should evaluate to [0, 1, 2].)

As #214 points out, it's also quite a good example of an exception to the Single Evaluation Rule — we get the thunkish behavior precisely because we evaluate the left macro operand once per iteration.

[masak]

This is easy, and doable today. As per #194, whoever does this also gets to pick one of the old example source files to remove.