Add allocators and instance initialization.

Adds class allocators and methods `alloc` and `__call__` for class
`Class` which are used to initialize new instances of the class.
Add initializer and hashing methods.
API: Add Set class.

Adds implementation of hash set and it's initial API.
Add list allocator.
Merge pull request #47 from peelonet/hash-set

Hash set implementation, allocators and initializers.