Fix: Allow an `h-card` in an `h-event`'s `p-location` field + add Ludorati's details to HWC Notts

It turns out that this was a bit of an oversight of mine - as called out by Chris Emerson on Twitter, I hadn't named Ludorati cafe as our destination.

Then, looking through the Microformats wiki, it appears that to embed the details of a place (i.e. add a p-name) you need an h-card.

We therefore need to extend our code to verify that there is an hcard in the location field, and then that it's valid.