Add two setters (alpha transparency) to Contour.

Implement options for the colorbar in Contour

Improve streamlines and quiver

Implement the vector field plots: stream lines and quiver in Stream

Implement draw_tri in Contour (uses a triangulation and wraps pyplot tricontour)

Implement FillBetween, Canvas::draw_triangles, Canvas::draw_triangles_3d, and other small improvements.

Add draw_rgb_or_rgba function to Image

Small improvements to InsetAxes

Implement InsetAxes