Separate Box IO API into a separate header/body.

include/tarantool.h

include/tarantool_lua.h

mod/box/CMakeLists.txt

mod/box/box.h

mod/box/box.m

mod/box/box_lua.h

mod/box/box_lua.m

mod/box/memcached-grammar.m

mod/box/memcached-grammar.rl

mod/box/memcached.m

mod/box/port.h

mod/box/port.m

mod/box/space.h

mod/box/space.m

src/admin.m

src/admin.rl

src/tarantool.m

src/tarantool_lua.m