* Add a unit testing framework in libnum/test/. Assertions are checked
against sparse sets of input values (a couple thousands for each
type), distributed fractally.
* Add performance tests for num16.
* Fix an overly ambitious substitution of /256 by >>8 in num16::mul,
which would give some incorrect results for negative results.
* Also fix an incorrect sign extension in the num16->num32 conversion.
* Express comparison-with-int operators in terms of the integer even
though some versions are faster when expressed in terms of the fixed-
point value. This is because the integer is frequently known at
compile-time.
* Add minDouble and maxDouble static members to each num type to
programmatically supply the bounds of the type.
