Chore: release v0.3.0

[jofas]

PRs:

• Use syn 2 #14
• Add support for String and enums #13
• Use full path to std::result::Result #11

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Issues:

• CI fails because gh-md-toc does not add backticks to generated output #24
• Add publish action #23
• Docs: links from proc macros to the crate root docs more precise #20
• full paths with leading :: on every import #19
• Docs: describe behaviour of FromStrAsJson in case type deserialises from a JSON string (opposed to an object or array, for example) #18
• Fix actions on main (clippy) #17
• Run build pipeline on PRs #16
• Document fact that serde_json needs to be imported by the user #12
• serde and serde_json dev-dependencies #10
• Delete TODO.md #9
• Remove codecov #8

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• Update changelog