[Chicken-users] ported Ephem egg to Chicken 5

[Rob Altenburg]

This egg contains bindings to the  libnova library which is "a general purpose, double precision, Celestial Mechanics, Astrometry and Astrodynamics library" available under the GNU LPGL.

See: https://github.com/RobAltenburg/ephem

None of the features have changed, but it no longer requires the SRFI-19 egg.

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Rob