Update CHANGELOG

CHANGELOG.md

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 # Changelog
 
+## v0.20.0 (April 27, 2023)
+
+- Bump syn to version 2, courtesy of @jonasbb [#227](https://github.com/TedDriggs/darling/issues/227)
+
+### Breaking Changes
+
+- Replace all occurrences of syn::NestedMeta with darling::ast::NestedMeta.
+
+- Replacement for the deprecated AttributeArgs:
+
+```rust
+// Before
+
+parse_macro_input!(args as AttributeArgs);
+
+// After
+
+match NestedMeta::parse_meta_list(args) {
+    Ok(v) => v,
+    Err(e) => { 
+      return TokenStream::from(Error::from(e).write_errors()); 
+    }
+};
+```
+
+- In GenericParamExt, `LifetimeDef` is now `LifetimeParam`.
+- In GenericParamExt, `as_lifetime_def` is renamed to `as_lifetime_param`.
+- Flag and SpannedValue no longer implement `syn::spanned::Spanned`.
+- The MSRV (minimum supported Rust version) is now 1.56, because of syn.
+
+### Deprecation Warnings
+
+In previous versions of `darling`, arbitrary expressions were passed in attributes by wrapping them in quotation marks.
+v0.20.0 preserves this behavior for `syn::Expr`, but as a result a field expecting a `syn::Expr` cannot accept a string literal - it will incorrectly attempt to parse the contents. If this is an issue for you, please add a comment to [#229](https://github.com/TedDriggs/darling/issues/229).
+
 ## v0.14.4 (March 9, 2023)
 
 - Add support for child diagnostics when `diagnostics` feature enabled [#224](https://github.com/TedDriggs/darling/issues/224)