v0.17.0: Release 0.17.0: matrices, vectors and tables.

Matrices, vectors and tables.

Added

• Matrix::new([[1, 2], [3, 4]]) draws values in square brackets. Each
  cell is a Txt from cell(r, c), row(r) or column(c);
  row_frame, column_frame and cell_frame give hidden outlines to
  fade in. .cell_width(px) leaves room for longer values.
• axes.vector(x, y) draws an arrow from the origin whose tip is two
  signals; v.to(x, y, seconds) moves it and .label("v") follows it.
• axes.apply_matrix(m, seconds) maps the plane through a 2 × 2 matrix:
  a transformed grid is drawn over the original, and plots, series,
  vectors and placed nodes move with it. axes.matrix() is the Mat2
  signal; Mat2::after multiplies and Mat2::det gives the determinant.
• Table::new takes the column titles and .row(..) adds rows.
  insert_row, push_row and remove_row slide the other rows into
  place, sort_by_column and sort_by move every row to its sorted
  place, and table.row(i) is a TableRow with a background to
  highlight it.
• Guide lesson 15, and the matrix_multiply, linear_map and
  table_sort examples.