Feature suggestion: In pattern input, allow + and - in place of H and 0

[jkboyce]

When writing long prime siteswap patterns, it's convenient to use + and - in place of H and 0.

For example, the longest prime pattern with 5 balls, max throw 7 is ++++1+-+++1++-++4-. We want to allow the user to input patterns in that format.

The algorithm will need to infer the value of H based on finding the minimum value that makes a valid pattern.