Fix OR in Journey patterns

Journey supported OR tokens right from the start (using the pipe character), they are translated into proper AST nodes. However, the rule for translating them into a regular expression was missing, so I added it.

I don't understand the router well enough (yet) to check if that's all that's needed to make them generally work. The code I actually started looking at, was the code for generating URLs, not sure if that works properly with OR literals in there. @tenderlove informed me, that he has some refactoring of said code pending, so I refrained from diving into it.

My main motivation for looking into this in the first place, was a conversation I had with @amatsuda about doing a spike on using [Mustermann](https://github.com/rkh/mustermann) in Rails to see if it would speed up url_helpers (it's really fast at expanding a URL pattern into a full URL).