mdtablefix 0.6.1

`mdtablefix` unb0rks and reflows Markdown tables so that each column has a uniform width. When the `--wrap` option is used, it also wraps paragraphs and list items to 80 columns.
Documentation 
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1. Prepare the state directory.
2. Define the session identifier.
3. Add the sidecar schema.
4. Wire the intake path.
5. Implement `SessionState::write_sidecar(&self) -> Result<(), IntakeError>` —
   writes the JSON sidecar file using `cap_std` filesystem primitives.
6. Implement
   `SessionState::read_sidecar(path: &Utf8Path) -> Result<Self, IntakeError>` —
   reads and deserializes a sidecar file.
7. Add `serde` and `serde_json` to the import list (both are already in
   `Cargo.toml`).