Services to compute ephemeris and related times.

There are two RDs in here: times.rd and res/apfs_new.rd (the latter
could be moved up, but that would break URLs).

Both of these used to wrap fortran programs, the sources of which we
still keep in src.  In 2025, we are porting things over to using erfa
and jplephem directly.  To make things work, you need to obtain
ds430.bsp from http://naif.jpl.nasa.gov/pub/naif/generic_kernels/spk/
and put it into the data subdirectory.  Use a different ephemeris
and results will subtly more.  Which is probably fine, but for now
we strive for almost-bitwise continunity with Helmut's code.