Parable DI 1.0.0

It's time! Finally a 1.0.0 release, locking the interface in place for at least a while.

Changes

• Completed the README.
• clear() no longer throws on a non-stored instance, since the expected result (that instance no longer being stored) is met.
• NotFoundException renamed to InstanceNotFoundException for clarity.
• Added unmap(string $requested): void to unmap and clear any mapped instance.
• Improved clearExcept() to use clear() so it also unsets any existing relationships.