v0.8.0 - Persistent storage

This release is a grab bag of support technologies to enable the underlying goal of enforced unique indexes.

• Switched from IOManager to FileManager which means all storage is persisted now. This is not crash safe. File interactions are designed to scale to a fixed maximum file handle count.
• Decided the primary key for storage is a Uuid, this will be the basic differentiator to route storage requests. At this time I'm not planning on supporting real tablespaces. If I change my mind, I'll have to plumb it in to this infrastructure.
• Have real integration tests using a non-feophant Postgres driver.
• Have the ability to profile the code and already found two places that were unneeded hot spots. "vec![]" is a code smell! You should be able to make a moderate guess on how big it will get.

Implemented but unintegrated code (which means I'll change it like crazy as I integrate):

• A lock manager based on weak refs
• BTree indexes