New file 'ephemera_common.h' contains declarations common to the 'ephemera' functions

git-svn-id: http://svn.savannah.nongnu.org/svn/avr-libc/trunk@2339 1084037a-409f-4a99-8160-1a4b3577d4c1
Modified 'equation_of_time' to more closely conform to the zeros of the 'full' equation.

git-svn-id: http://svn.savannah.nongnu.org/svn/avr-libc/trunk@2340 1084037a-409f-4a99-8160-1a4b3577d4c1
Modified 'solar_declination' to conform more closely to the zeros of the 'full' equation.

git-svn-id: http://svn.savannah.nongnu.org/svn/avr-libc/trunk@2341 1084037a-409f-4a99-8160-1a4b3577d4c1