Filter distances based on prior knowledge of attitude

[taldcroft]

We have thought of two ways to filter:

• a radial filter around an attitude
• a band in sun pitch

This issue is coupled with the ability to reduce the number of stars required to find a match (down to three).

Reducing the requirement to just two stars would require larger changes to find_attitude, such as filtering on the roll between the two stars, or their magnitude difference.

[jeanconn]

Closed by #31