0.5.0 Complete rewrite; constant and function constructors, generic anonymous functions and objects

[vudaltsov]

The library was rewritten from scratch with a new philosophy in mind:

Changed

• Extract types constants to global constants: types::int -> intT.
• Extract types methods to functions: types::intRange() -> intRangeT().
• Make Type classes public.
• Rename TypeVisitor to Visitor, pass types as objects without destructuring.
• Rename TypeStringifier to Stringify, make it abstract.
• Rename DefaultTypeVisitor to Fallback.

Added

• Reduced visitor that expresses some types via the others, reducing the number of Visitor methods to implement.
• Support for generics in anonymous functions and objects.

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This discussion was created from the release 0.5.0 Complete rewrite; constant and function constructors, generic anonymous functions and objects.