Implement logic required to shortcircuit to destination filter

[cassava]

This is actually something I've wanted to do for a while, so it will probably land in it's own package.
It's similar to a radix tree, but it's not the same, I don't think.

[cassava]

See the package github.com/goulash/short when it's ready.

[cassava]

At the moment, I've implemented an internal package shortry which kind of does the trick. The problem is that the API and functionality is not entirely clear: what exactly should be a valid shortcut to what?

[cassava]

I won't fix this at the moment. Need to think about it.

[cassava]

I'm closing this because I don't see the need to make things unnecessarily complex at the moment.