planets: replace acos() with arccos() to catch complex solutions.
Add module math with safe arccos/arcsin functions.
Update copyright.
planets: ensure argument of arccosine lies in [-1,1].
sun: sunpos_la(): use calc_deltat_approx() to test SolTrack.
Finding a solution for comets with hyperbolic orbits
Update copyright.
solvers: minimum_solver() better recognition of min outside range.