webmention

Right now we only use a poor-man cache - so we don't load the same data during one runtime but the next runtime we will load it again.
An idea would be a cacheFor() method on the client which you can call in your own service provider and pass in a value compatible with Cache::remember() and false to don't use the Laravel cache.

As cache-key I would use something like `webmentions.md5(dom

Current behavior:

$ whim help verify
Usage: whim verify
$ 

We should expand this into more complete documentation, like the other commands have.