document _selector and _cell for mongo cube builder
document _selector and _cell for mongo cube builder

ubreddy/cubes,she11c0de/cubes,cesarmarinhorj/cubes,zejn/cubes,zejn/cubes,jell0720/cubes,she11c0de/cubes,she11c0de/cubes,noyeitan/cubes,zejn/cubes,noyeitan/cubes,jell0720/cubes,pombredanne/cubes,cesarmarinhorj/cubes,ubreddy/cubes,cesarmarinhorj/cubes,jell0720/cubes,pombredanne/cubes,ubreddy/cubes,pombredanne/cubes,noyeitan/cubes