v0.9.0

• Breaking: Increase MSRV to 1.70.0 (minimum version to run the test suite)
• Breaking: Remove non-canonical PartialOrd implementation (#1)
• Make partial_cmp() an inherent method of Serial
• Add precedes(), precedes_or_eq(), succeeds(), and succeeds_or_eq() methods
  to replace now missing <, <=, >, and >= operators
• Add postcard feature