Release v0.20.0

What's Changed

• Read dimensions other than variable and region from external repo by @korsbakken in #415
• Add CLI command to validate scenario data file from definitions by @dc-almeida in #419
• Add tier as named attribute for VariableCode by @dc-almeida in #420
• Added explicit encoding to all open statements. by @korsbakken in #407
• Add dimensions option to CLI validate-scenarios by @dc-almeida in #421

Full Changelog: v0.19.1...v0.20.0