docs: public IStringBuffer deleteCharAt( int idx )
      {
          if ( idx < 0 )
              throw new IndexOutOfBoundsException("idx < 0");
          if ( idx >= count )
              throw new IndexOutOfBoundsException("idx >= buffer.length");
          
          //here we got a bug for j < count
          //change over it to count - 1
          //thanks for the feedback of xuyijun@gmail.com
          //@date 2013-08-22
          for ( int j = idx; j < count - 1; j++ ) {
              buff[j] = buff[j+1];
          }
          count--;
          
          return this;
      }