Add delete method and context manager integration

This release adds a delete method to the Manifester class and makes Manifester a context manager. Both changes facilitate cleanup of subscription allocations after a Manifester run completes.

What's Changed

• Add delete method to Manifester class by @synkd in #9
• Add basic context manager functionality by @JacobCallahan in #10

Full Changelog: 0.0.4...0.0.5