This picks up the major work of allowing multiple heap implementations
and enable dlmalloc as an alternate heap to the simple existing one
(now called 'miniheap').
Also added a novm page allocator for memory management on systems too small
or missing an mmu to have a vm. Not much more than a simple bitmap allocator
that the heap pulls from. Allows for other heaps and/or users of physical
memory to coexist and span multiple banks of memory.
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