"FCModel 2" non-unique-instances branch

[marcoarment]

Just pushed the first commit e0f9b3d3 of what might be called "FCModel 2" to the "non-unique-instances" branch. This is a big, likely-breaking change that applies a lot of lessons learned since the original design:

Instances are no longer tracked or kept unique in memory. All instances are "detached".

• You can have two instances in memory of the same logical model (same table and primary key).
• Changes made to a model object or table won't affect any other copies in memory.
• If you want your interface to react to changes, you must reload any data in response to FCModel's change notifications.
• dataWasUpdatedExternally, reloads, and conflict resolution are no longer necessary and have been removed.
• allLoadedInstances is no longer possible and has been removed.
• Transactions are now supported, although limited. (Rollbacks don't revert changed models in memory.)
• Autoincrement, formerly deprecated, is now removed and will raise an exception.

All saves and deletes are expected to succeed. Saves shouldn't unexpectedly fail or be blocked.

• Removed should/didInsert/Update/Delete, saveWasRefused, saveDidFail. To customize behavior, override save and call [super save] from the subclass.
• FCModelSaveResult is removed. delete now returns void and save now returns a BOOL to indicate whether changes were made.
• Saves and deletes that fail from database errors now raise exceptions. lastSQLiteError is removed.
• All FCModel exceptions now have name FCModelException.
• saveAll has been removed. Saves should happen intentionally, right after you change the data.
• Custom serializations for NSURL, NSDate, etc. have been removed to avoid a lot of subtle bugs and inconsistencies between formats.

Notifications have been simplified to just a single FCModelChangeNotification for any change to a table.

• FCModelInstanceSetKey has been replaced by FCModelInstanceKey and will always be one instance if known, or unset for many/unknown.
• Notification-batching functions are now redundant and have been removed since transactions also batch notifications.

Take a look and see what you think so far. What other changes should we consider now that we're breaking things?

PLEASE don't ship any apps with this yet.