old tests type.is are useless now
makes safe Union.dispatch
removed useless variables
v0.2.0

- add `isKind, getKind` functions, fix #29
- add to `struct` an assert on `props` argument, fix #30
- add sweet.js macros for all combinators, fix #32
- add a `defaultDispatch` function to `union` combinator, fix #33
- add overloading to `func`, fix #35

**BREAKING**

- now the kind of Any and all primitives is 'irriducible' fix #34
- uniform `Any` and primitives, export `irriducible` function, fix #34
- group all util functions in a `util` namespace, fix #36