v0.2.0: introduce StructEnum and SafeEnum

What's Changed

• Refactor mtmap and add mtkey for better readability by @huykingsofm in #11
• Introduce safe enum + serde by @huykingsofm in #12
• fix typo readme by @huykingsofm in #13
• fix readme by @huykingsofm in #14
• refactor documentation by @huykingsofm in #15
• Create FUNDING.yml by @huykingsofm in #16
• update FUNDING by @huykingsofm in #17
• add struct enum by @huykingsofm in #18

Full Changelog: v0.1.0...v0.2.0