[Virtual memory compression] status update

[Paavo-Einari Kaipila]

Hey

Sorry everyone, I've been a bit shy because there hasn't been much to
showcase until now. But anyway, I'm on schedule and the disk even
works now!

The repo resides here and the commit
4f6ac56fd5fc4ffb4f8a36669579ae83e89d0103 is "guaranteed" to work.
https://github.com/pavetheway91/freebsd

You may create a compressed memory disk with mdconfig:
mdconfig -t compressed -s 10m

Zlib is the only supported algorithm at the moment. I'm looking
forward to adding zstd and lz4 soon.

I'd like to get some input on few questions:
- Should zlib be included in the final product just in case if someone
doesn't have lz4 or zstd in their kernel?
- Should I make a separate stream for each cpu core or stripe across
multiple devices when swapping?

And special thank you for my "third mentror" markj who has been extra helpful.

-Pave