port libvips

Good day

This is the first time I mail this mailing list. I hope not the last
time.

I have managed to make PeerTube run on my OpenBSD 6.6 beta home server,
so I wish to try to propose a port for it. But first, PeerTube has
libvips as a dependency, which is not in ports. So as a training for a
much harder thing, here is my proposed port of libvips-8.8.2, which I
have been able to build on said server via the port system.

Vips is a fast image processing library, and as a result, I put it in
multimedia category.

The library has some optional dependencies (it can support quite a lot
of image formats if you have support libraries on the machine). Which I
don't really know how to indicate.

I am waiting for comments.