Change Number bounds from Int to Scientific.

[tvh]

This allows validation on all values regardless of size of maxBound.

If this is merged, the code from PR #17 would change with sane bounds.

[hesselink]

In principle this sounds good, I think. However, it seems the Show instance for Scientific is different from Int, in that it always prints with one decimal place (1.0 instead of 1). This will change e.g. the documentation generated by rest-gen, which might be confusing (seeing 1.0 for an integral type). @bergmark What do you think?

[bergmark]

We have a floatingOrInteger check in rest-gen for dealing with this difference, does this change hit some other code path?

I'd prefer to have two AST items for floating and integral types. I use integrals pretty much exclusively with json-schema. It's a breaking change either way.