v0.12.0

• Increased parsing performance by more than 100%
• Remove type annotations from code examples in README.md, because they confused beginners
• The Record tagged_t payload got a new data structure
• Fixed S.json type
• Add validation of Literal struct values on serializing
• When serializing/parsing Literal struct value in Unsafe mode it'll always return literal value even if provided something else.
  Example: 123->S.parseWith(~mode=Unsafe, S.literal(String("foo"))) === Ok("foo")