Axiom

- Upgraders can now safely upgrade reference attributes.
- The batch process is no longer started unless it's needed.
- Removed use of private Decimal APIs that changed in Python 2.5.2.

- "axiomatic start" changed to use the public interface to twistd's
behaviour instead of relying on internal details.
- Store now uses FilePaths to refer to its database or files directory.
- Automatic powerup discovery is now a feature of powerups rather
than of axiom.dependency.
- Stores now record the released versions of code used to open them.
- "axiomatic upgrade" added, a command for completely upgrading a store.
- Removed no-longer-working APSW support code.

- Substores and file storage for in-memory stores are now supported.

- A bug where exceptions were raised when tables were created concurrently is
now fixed.

- Added the beginnings of a query introspection API.

- Added a 'postCopy' argument to
upgrade.registerAttributeCopyingUpgrader, a callable run
with the new item after upgrading.

- Fixed a bug where user store insertion/extraction failed if a
SubScheduler was installed but no TimedEvents existed.