Merge branch 'small'

include/memory.h

src/lib/small/CMakeLists.txt

src/lib/small/lf_lifo.h

src/lib/small/mempool.c

src/lib/small/mempool.h

src/lib/small/region.h

src/lib/small/slab_arena.c

src/lib/small/slab_arena.h

src/lib/small/slab_cache.c

src/lib/small/slab_cache.h

src/lib/small/small.c

src/lib/small/small.h

src/log_io.cc

src/memory.cc

test/unit/CMakeLists.txt

test/unit/arena_mt.c

test/unit/arena_mt.result

test/unit/mempool.c

test/unit/region.c

test/unit/slab_arena.c