v0.5.0

There were enough wires to rip up that I'm mashing all of these changes
into one big changeset for the v0.5 update.

The big changes include:

• Remove the Runner, move all the common iterative logic to a
  templated Transform virtual base class, from which Rigid and
  friends derive.
• Remove vendored upstream dependencies (other than gtest). Managing
  vendored dependencies was a big pain. Instead, I'm trying out
  "components", e.g. the jsoncpp functionality is included as a
  component that requires an external jsoncpp to be present. We'll see
  how that goes.
• Remove all logging, for now. I might add it back (via the component
  mechanism mentioned above) but I'm not sure. While it's useful for
  keeping tabs, it mucks up the business part of the code a lot. I have
  a vauge idea about adding callbacks into the main cpd loop and using
  those for logging, but nothing's there yet.
• Refactored tests and fixtures, to hopefully make it easier to
  modify/etc in the future. This rewrite mostly happened becuase I
  couldn't bring myself to rip apart the v0.4 test suite without just
  redoing it all.

Note that a lot of the business code in this rewrite was not touched —
this is more of an interface change than anything that affects the
actual math.