fix: switch to @iarna/toml as toml parser, handle raw dates in datetime field (#715)

packages/docs/content/docs/collection-overview.mdx

@@ -65,9 +65,11 @@ You may also specify a custom `extension` not included in the list above, as lon
 
 - `yml` or `yaml`: parses and saves files as YAML-formatted data files; saves with `yml` extension by default
 - `json`: parses and saves files as JSON-formatted data files; saves with `json` extension by default
+- `toml`: parses and saves files as TOML-formatted data files; saves with `toml` extension by default
 - `frontmatter`: parses files and saves files with data frontmatter followed by an unparsed body text (edited using a `body` field); saves with `md` extension by default; default for collections that can't be inferred. Collections with `frontmatter` format (either inferred or explicitly set) can parse files with frontmatter in YAML or JSON format. However, they will be saved with YAML frontmatter.
 - `yaml-frontmatter`: same as the `frontmatter` format above, except frontmatter will be both parsed and saved only as YAML, followed by unparsed body text. The default delimiter for this option is `---`.
 - `json-frontmatter`: same as the `frontmatter` format above, except frontmatter will be both parsed and saved as JSON, followed by unparsed body text. The default delimiter for this option is `{` `}`.
+- `toml-frontmatter`: same as the `frontmatter` format above, except frontmatter will be both parsed and saved only as TOML, followed by unparsed body text. The default delimiter for this option is `+++`.
 
 ## Frontmatter Delimiter