= [,] command
        .shift the text of the line compressing continued spaces
         to a space char.
         shift stop when n space char is dropped.
        .for margined file,only data in the margin is shifted.
        .n of x[n],xx-xx[n] is shift count,default is same as tab count.
         tab count is set by TAB command and default is 4.
         xn,b.s pattern is not supported.
         effect of b,s parameter is same as "(" command.

        .space compressing shift

            [[     |1234567890ABCDEFG
            0002000|  34567890  CDEFG
            0003000|    567890  CDEFG
            0004000|     67890  CDEFG
            0005000|  34  78  AB  EFG
            [[     |  34  78  AB   FG
            ]]     |  34  78  AB   FG
            0008000|1234567890ABCDEFG
            0009000|1234567890ABCD
            0010000|1234567890A
            ]]     |123  67  0A  DE
            [5     |1   5   90   DEFG
            ]3     | 12   7890ABCDE
        ===>
      [[4   0001000|1234567890ABCDEFG
            0002000* 34567890 CDEFG
            0003000* 567890 CDEFG
            0004000* 67890  CDEFG
      [[4   0005000* 34 78 AB EFG
      ]]4   0006000* 34 78 AB  FG
            0007000*      34 78 AB FG
            0008000|1234567890ABCDEFG
            0009000*  1234567890ABCD
            0010000*    1234567890A
      ]]4   0011000*    123 67 0A DE
      [5    0012000*1 5 90  DEFG
      ]3    0013000*    12 7890ABCDE