Auto-generation of blog post permalinks (wincent.dev, f71a66b)

It would be nice if we could normalize everything to ASCII but Iconv can't be trusted to do the same thing across platforms so instead opt for an even lossier approach: basically everything that's not ASCII is converted into a hyphen.

We perform one database query to see if there's a clash to make sure that we generate a unique permalink each time. This would be racy in a multi-user scenario but it's envisaged that I'll be the only one publishing articles so this is probably fine.

Signed-off-by: Greg Hurrell <greg@hurrell.net>