v0.9.0

Full Changelog: v0.8.0...v0.9.0

• Add support for custom error type in reduce action. String will be used if not set.

%error <ErrType>;
...

A: token0 token1 token2 {
  return Err( <ErrType>::new() );
};

match parser.feed( ... ) {
    Ok(_) => {},
    Err(e) => {
        match e {
            rysty_lr::ParseError::ReduceAction( err_from_action ) => { ... }
            _ => {}
        }
    }
}

• clean some doc comments