Most useful for 64-bit values as only one instruction is needed to move
the data around rather than two, but could be slightly faster for 32-bit
as the addressing is simpler (needs profiling).
Bools turned out to be a problem to due to me wanting any non-zero value
to be treated as true thus had to expand them out as well as the
floating point <-> integral conversions.
Rather than specifying that the conversion should be skipped, it now
specifies the mode of the conversions (with 0 being no conversion). This
is in preparation for boolean conversion.
Not all possibilities are supported because converting between int and
uint, and long and ulong is essentially a no-op. However, thanks to
Deek's suggestion, not only are all reasonable conversions available,
conversions for all widths are available, so vector conversions are
supported.
The code for the conversions is generated.
