Set a maximum value, for small numbers

[dimbleby]

Setting a maximum and minimum value for more numeric types, where that's possible.

Would be nice to do this for more types, but while we have nothing better than f64 in which to write these limits, can only do it for small numbers. I suppose we somehow want these fields to be of the same type as the integer being described, but that's more type gymnastics than I'm capable of right now.