Gathered some constant terms from equation_of_time.c and solar_declination.c,  into ephemera_common.h

git-svn-id: http://svn.savannah.nongnu.org/svn/avr-libc/trunk@2342 1084037a-409f-4a99-8160-1a4b3577d4c1
Pulled the calculation of solar noon from sun_rise.c and sun_set.c, creating new function solar_noon().

git-svn-id: http://svn.savannah.nongnu.org/svn/avr-libc/trunk@2343 1084037a-409f-4a99-8160-1a4b3577d4c1