Merge PR for #34, add or_else_any_method explicit handlers

[nilslice]

This PR builds on #34, adding explicit route handler for non-match patterns using the not_found and not_found_async methods.

It also modifies the worker-sandbox Worker to narrow its match handlers to more specific HTTP methods to allow for better testing of wildcard patterns and not_found handler.

[nilslice]

@fkettelhoit - if possible, it would be great to get your review on this to make sure it captures all of what you were aiming to have supported with your PR.

[fkettelhoit]

@fkettelhoit - if possible, it would be great to get your review on this to make sure it captures all of what you were aiming to have supported with your PR.

Looks good! I was thinking a bit about how the not_found case might be generalized, the result is PR #47. But I am honestly not sure whether that would add significant value over the more specific version implemented here, in my opinion either would be fine.

(I think there is a larger issue at play here: How much should be handled directly in a single router vs. composing multiple routers? Thanks to the functional nature of the router, it is easy to map the result of one router and use another router for any 404 response, for example, which can already solve most catchall cases. But there is still value in providing an API that solves most common situations in a single router, in my opinion, because compositions of different routers are not always the most obvious solution. I would say that all in all the current PR strikes a good balance there.)