Humphrey v0.2.4

This release makes no changes to the actual functionality of Humphrey, but includes some strong performance optimisations and updates the back-end core crate to the latest version.

What's Changed

• Optimised efficiency of both crates (+10.5% performance) by @w-henderson in #12
• Humphrey Core 0.2 by @w-henderson in #20

Full Changelog: 0.2.3...0.2.4