Merge branch 'small-submodule' into 1.6

.gitmodules

src/lib/CMakeLists.txt

src/lib/small

src/lib/small/CMakeLists.txt

src/lib/small/README

src/lib/small/ibuf.c

src/lib/small/ibuf.h

src/lib/small/lf_lifo.h

src/lib/small/lifo.h

src/lib/small/matras.c

src/lib/small/matras.h

src/lib/small/mempool.c

src/lib/small/mempool.h

src/lib/small/obuf.c

src/lib/small/obuf.h

src/lib/small/quota.h

src/lib/small/region.c

src/lib/small/region.h

src/lib/small/slab_arena.c

src/lib/small/slab_arena.h