Provides a global allocator using the umm_malloc library.
umm_malloc is a small and simple malloc designed for embedded systems.
It is able to allocate and free quickly with limited memory fragmentation.
All allocations form this allocator are aligned by 8 bytes. Requesting a larger alignment is not implemented and will panic.
umm_malloc has features for collecting metrics and detecting heap corruption,
which could be exposed conveniently with cargo features.
An implementation of memalign could be added to umm_malloc.