The hierarchy-specific tests from the transform tests have been moved
into the ecs tests and the transform tests renamed appropriately. As
part of the process, hierarchies can now have a null type (ie, no
additional components maintained by the hierarchy). This should make
sorting out the issues highlighted by sbar a bit easier.
It should have always been here, but when I first created the hierarchy
and transform objects, I didn't know where things would go. Having two
chunks of code for setting an entity's parent was too already too much,
and I expect to have other hierarchy types. Doesn't fix the issues
encountered with sbar, of course.
As the bookkeeping data is spread between three arrays, sorting a
component pool is not trivial and thus not something to duplicate around
the codebase.
As an implementation detail, inserting null hierarchies (src hierarchy
is null) is supported for ease of hierarchy construction from data. No
component data is copied, only the child and parent indices and counts
are updated.
While the libraries are probably getting a little out of hand, the
separation into its own directory is probably a good thing as an ECS
should not be tied to scenes. This should make the ECS more generally
useful.
