Structs
A linked list stored in contiguous memory allowing random access through ids.
Similar to Vec except that it is indexed using an Id rather than an usize index.
if the stored type implements Default, IdVec can also use the set(…) method which can
grow the vector to accomodate for the requested id.
Use this as the NullId type parameter of the freelist if the id type is an option,
to use
Option::None as the null id value.Traits
A trait that defines how to choose the null (or invalid) Id.