Add two new data types: DCOUNTER and DDERIVE, which resemble
COUNTER and DERIVE, but take double precision floating point
number as an argument. Like it or not, the world as we know it
is not described by integer numbers, not even the real numbers,
it's complex amplitudes, folks. But well, we don't onserve
amplitudes directly, so real numbers are the closest bet that
we have at the moment.

This is still WiP, documentation is coming.