0.6.1: Python multithreading, unit vector querying, beta angle

New features

• Introduce Unit Vector functions by @gwbres in #446
• Add beta angle computation by @ChristopherRabotin in #452
• Enable Rust multithreading speeds for Python: search for the many keyword in the functions by @ChristopherRabotin in #454

Dependencies

• Update tabled requirement from =0.19 to =0.20 by @dependabot in #448

Full Changelog: 0.6.0...0.6.1