Better allocator function

[p0nce]

Lua has the following single function:

typedef void * (*lua_Alloc) (void *ud, void *ptr, size_t osize, size_t nsize);

also recommended in some articles, and the one usef in msf_gif.

[p0nce]

Dennis has a design for allocator here: https://github.com/dkorpel/dconf/blob/master/dconf24/allocator.d, linked list of increasing-size pages, GC-compatible, not @nogc