Release 3.7.0

• Remove a big bunch of panic possibilities in serializers and deserializers.
• More thorough and correct signature checks.
• Limit container recursion depth to avoid stack overflows.
• Add fuzzing to CI.
• Signature::from_str_unchecked now const.
• Value::to_owned now a public API.
• Add more Error variants:
  • OutOfBounds.
  • MaxDepthExceeded.