Added Handler.pattern. Tweaked Handler.__str__() to handle strings with single-quotes in them.

Handler.pattern should've been in there from the start. Derp. 6_9

Handler.__str__() now calls repr() on strings, rather than having single quotes around the formatting tokens. This ensures that characters in a Handler's event or pattern string that should be escaped in the string representation (e.g. single-quote, newline), will be.