code: public Matrix insert(Matrix that, int rows, int columns) {
          return insert(that, 0, 0, 0, 0, rows, columns);
      }
docs: Inserts a given {@code that} matrix (B) into this matrix (A). The original
  values are overwritten by the new ones.
  
  @param that the matrix to insert
  @param rows number of rows to insert
  @param columns number of columns to insert
  @return a matrix with the parameter inserted into it