Add cmake to exotic tests.
Move cmake files into c++ subdir.

The idea behind the directory organization was that we might have official implementations for other languages in other top-level directories, as siblings to the c++ directory. It seems implausible that we'd use CMake as a meta-build-system over all of these.

Another reason for this change is that the release tarball actually contains only the c++ subdirectory. We probably want to include cmake files in the release.
Include cmake files in automake dist.
Update release script to build Windows package.
Resolve TODO(now|soon) and remove KJ_DBG.
Apparently distcheck and dist-zip will stomp each other if run in parallel.
Improve release script's windows build.
Revamp installation docs, in particular to include MSVC info.
Tweak release.sh some more.