Add empty lines for clearer console output.
bug fix: memb_init block size must >= 4, otherwise size_t may not hold all required array index.
bug fix: memb_aloc index will go out of range while allocate 1 block.
change: variable names.
change: not existed blocks are moved, so used/none/free is placed at last row, this gives 1/2 max allocatable block size.