Add working function to compute kepler elements

Some clients are interested in the kepler elements, for example if
one wants to for example draw an orbital path. This reworks the
osculating elements structure to use traditional keplerian
elements only and enables the conversion of state vectors (produced
by vsop et.al. into kepler elements).
Remove debugging code
Merge pull request #5 from lorrden/master

Working function to compute osculating elements