Support a more complete (and simple) requirements gathering mechanism,

and add support for binary operations.

This version of requirements generation simply generates every numeric
size within a provided range, and then will reject trait implementations
that rely on values outside this range. It should be a little more easy
to reason about, and easier to make local changes as I (inevitably) need
to modify rules.

src/unsigned/mod.rs

@@ -1 +0,0 @@
-mod u192;