mdds 0.7.0 on master

[Kohei Yoshida]

Hi there,

FYI, the master branch now requires mdds 0.7.0 to build. This should
not be a problem for those who use internal mdds, but for those who
use the system mdds, please be aware of this.

Actually, at the moment, it should build fine with mdds 0.6.0, but
soon I'll start using bits that are only available in 0.7.0, which
causes a build failure if you build with the older versions.

Best,

Kohei