v0.20.0

What's Changed

• update copyright by @cqc-melf in #192
• remove docs build from release workflow by @cqc-melf in #193
• update pytket version by @cqc-melf in #194
• Constrain to pytket 1.x. by @cqc-alec in #195
• Update version and changelog for 0.20.0 release by @cqc-alec in #196

Full Changelog: v0.19.0...v0.20.0