v0.2.0

I've never made any releases for apfsprogs before because it was mostly
intended for my own use, to help me test the driver. But at this point a
few of the tools might actually be useful to others, and even the mkfs
is probably mature enough to be safe, so I guess I should start. I'm
using 0.2.0 because all of the man pages have been set to 0.1 until now.