Add sample regexps

[javallone]

Just a simple list of expressions to demonstrate with. Probably best to wait until after #7 is complete.

[javallone]

Include the "Check if a number is prime" example: ^1?$|^(11+?)\1+$

[dave1010]

Here's one that looks nice (matches URLs)

^(([^:/?#]+):)?(//([^/?#]*))?([^?#]*)(\?([^#]*))?(#(.*))?