Hohmann transfer calculations for Earth to Mars migration

Added three new calculations:

1. Distances between stars (using start-chart coordinates)
2. Apparent magnitude of stars from other stars
3. Hohmann Transfer Orbits

Hohmann transfer orbits allow migration from a lower to a higher orbit or vice-versa. When used for interplanetary travel, these are solar orbits, but this kind of orbit can be used to move satellites to a higher altitude (or bring them back to a lower one).

The distances between stars is calculated from star-chart coordinates by first converting from the spherical coordinate system to a rectangular one. The apparent magnitude of the two stars (from each other) is calculated at the same time.