Replace 'void *' with 'char *' in most places

include/assoc.h

include/box/box.h

include/log_io.h

include/pickle.h

include/recovery.h

src/box/bitset_index.cc

src/box/bitset_index.h

src/box/box.cc

src/box/box_lua.cc

src/box/hash_index.cc

src/box/hash_index.h

src/box/index.h

src/box/request.cc

src/box/request.h

src/box/space.cc

src/box/tree_index.cc

src/box/tree_index.h

src/box/tuple.cc

src/box/tuple.h

src/box/txn.cc