Include lots of example rules

The new version of Zendo includes cards with example rules, and adjustable parameters. It's a good way to stop new players from making rules too hard.

Here are some attributes of an input to consider for rules:

* letters, digits, space, punctuation
* upper case or lower case
* zero, at least 1, exactly 1, exactly 2, exactly 3 of something
* more of a certain type
* one type before another type
* forward / reverse symmetry