Increase the quantity of property tests

[Acaccia]

Fixes #54

Now we have a huge load of tests, on all kind of ranges of integers, in all configurations.

Good thing, most stuffs work.
Bad thing, the multiplication doesn't.

UPDATE:
Finally everything works:

• mul-uint had a stupid mistake in the case where the sum of leading zeros was 127 and b is odd
• mul-int overflow detection didn't work. The new algorithm does.
• there was a mistake in the proptests of sqrti-int.

[obycode]

Just minor comments. Looks great. Thanks for fixing this!

[obycode]

LGTM!