…on and singleton. No optimizations yet. All tests pass.

See cython/cython#2425

…naive version so far. Hopefully we can get better still.

This was a pretty big win, getting us 9-13% faster on the
externalization benchmarks compared with the last commit.

…place) so it can be a tuple. This is again slightly faster.

…ther 1-2% on extern.

…eading underscores, rename our private module back to private again.

This nets us a 4% improvement or so in externalization, maybe a tiny
slowdown in internalization (but I expect that to be fixed when I type
that module).

We could do better, but the class attribute _ext_excluded_out_ and the
like are slowing us down, and we have some code that doesn't keep
their usual types (mostly in housing). A metaclass may be able to fix
that, because they all seem to be defined at the class level.

Define them as an instance, make an accessor function, type the result
of the accessor in the pxd. This avoids needing to get the type in the
python file, which is what causes the leading underscore problems.

This avoids the need for re-enumerating all the constants while still
being direct access (yay!). Speeds things up by another percent or two
in datastructures.py.

…ment on the benchmarks, it appears.

…ning bottlenecks

Two changes of note:
- notify_modified alias was removed. I couldn't find any uses of it on github
- eventFactory was removed from notifyModified. I couldn't find any
  uses of it on github.

These are both easy to add back if needed.

…nary with a warning.