SAC and allocation shouldn't co-exist

[LeoVen]

CMC_SAC makes a collection to have a fixed buffer size, possibly avoiding allocations, but the _new() function allocates the struct anyway. This can be good if the buffer size is huge and wouldn't fit on the stack.

• [ ] Find a way to avoid having malloc, free, etc. in the code whe CMC_SAC is defined
• [ ] Decide what to do with _new() and _init()