This means that the component id used for hierarchy references must be
passed to Hierarchy_New and Hierarchy_Copy, but does all an entity to
have more than one hierarchy, which is useful for canvases (hierarchies
of views) in the 3d world (the canvas root would have a 3d hierarchy
reference and a 2d (view) hierarchy reference).
While simple component pools can be cleared simply by zeroing their
counts, ones that have a delete function need that function to be called
for all the components in the pool otherwise leaks can happen.
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.
It doesn't check that the entity itself is valid, but it does at least
check that the index fetched from the sparse array is valid. Fixes a
segfault when a valid entity never had the component.
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.
