* `property`: fixed certain implicit conversions failing

* fixed broken typematch for unsized arrays after recent fix
* API: added `sc_type_is_unsized` function, allowing to query if a type is unsized, as element-count will now always return 0 for unsized types
* added `'unsized?` method for `type`
* added `unsized?` static operator to check for an unsized type at compile time

* `Map`: more fixes for unique value types

* `enum`: fixed `apply` returning no values
* `Map`: fix for inserting unique values

* fixed unsized `array` and `vector` types generating huge types

* `Set`: fixed `'insert` returning the wrong index if a value was newly inserted

* `enum`: method `'apply` does not call function argument for default branch

* `enum`: added `'apply` method that allows to call an inline for all payload branches

* `enum`: only set special methods when there are no user defined versions

* API: added `sc_anchor_new`

* smaller fix to `Set`

* fixed `swap` accidentally moving arguments
* `Set`: `insert` returns a reference to the inserted key
* fixed `Set` operations for unique values

* `Map`, `Set`: added support for specifying custom hash function

* added hashing support for `Nothing`, `Rc` and `Enum`

* `Map`: singled out `Set` class into its own `Set` module

* removed getattr access error from traceback

* `Enum`: small simplifications, improved test

* implemented `==` for `Nothing` and `Enum`

* moved `-->` operator from itertools to `chaining` module
* itertools: added `permutate-range` generator

* more work on tests