- added `Struct.extend(props, [name])`, fix #55
- added built-in immutable updates, fix #31

**BREAKING**

- change `dict(B)` combinator to `dict(A, B)` where A is the set of
keys, fix #54
- removed `util.isKind`
- removed `util.isType`, use `Type.is` instead
- refactoring of `func`. Now is a proper type combinator. fix #42
- removed `options.update`