Type - A Dynamic Type Library

Data & Type ==> Implementation

Key Concepts:

    - Data: Anything you can point at (void *).
    - Type: A name (const char *) and a specification (typically a structure).
    - Implementation: Any instance satisfying a type specification (void *).
    - Type Tag: A map between types and their implementations.

General Usage:

    1 - Data is associated with a type tag. There are a couple of ways to
    accomplish this. Two common ones are to add a pointer to a type_tag
    structure (inside of data), or use the global API which associates data
    with a type_tag structure.

    2 - A type is associated with its implementation. This is done using
    type_tag_attach(...). Once a type has an implementation attached it can be
    acquired and used.

    3 - Retrieve and use the type implementation using type_tag_acquire(...).
    If, for example, the implementation is a structure of callbacks:
    impl->callback(self, ...).

    4 - Release the type implementations using type_tag_release(...).

    5 - Detach the type implementation using type_tag_detach(...).

Utility macros are provided to ease the burden of the acquire, use, and
release cycle: type_tag_with(...) and type_with(...).