Added the ability to specify the result values delivered when conversions

Added the ability to specify the result values delivered when conversions
from floating-point to an integer format raise an invalid exception.
For the provided specializations (8086 and RISC-V), changed the result
of converting a negative floating-point value to an unsigned integer
format to now be zero.  (Also renamed `shiftCount' inside functions to
`shiftDist'.)