The API is now hidden behind functions. The GC struct can have an
unstable layout without affecting any compiled binaries (users of
Universal Service or collectors hidden behind the API). The
collectors can be called directly if desired.
The API now allows for different allocation flags. These will be
used in future extensions (like weak pointers). For now none are
used.
Tests are compiled for each collector. I can't think of a good
solution that will encompass everything I want to write, but for
now this will work on POSIX systems.
