util: Add mm, an interface to memory managers.
tests/simple_fixture.hpp: Provide MM as well as Mpool.
util: Convert a large chunk of util to use MM instead of Mpool. (See below)

Basically everything that depends on bytestr or list.
util/array: Update to use Memory Manager.
uil/hash, util/cfgmap: Update to use Memory Manager.
various tests: Change (void) to () in C++ code.
util/decode: Update code to use Memory Manager.
util/mm_mpool.c: Add assert.
util/dso: Update to use Memory Manager.
util/strwspc.c: Fix documentation typo.
util/file: Update to use Memory Manager.
util/flags: Update to use Memory Manager.
util/logformat: Update to use Memory Manager.
util/path: Update to use Memory Manager.
util/mpool_lite: Add mpool_lite, a simple memory pool.
util/mm_mpool_lite: Add mpool_lite to mm adaptor.
util/mm: Minor cleanup.
util/mm: Change return type of ib_mm_register_cleanup() to ib_status_t.
util/mm: Additional documentation on cleanup functions.
vector: Use new memory manager and lite memory pools.