FovVideoVDP 1.2.1

• [Python] Extra channels (alpha, depth) are now ignored.
• [Python] Better handling of grayscale images.
• [Python] Fixed the ppd calculations for steep viewing angles when the gaze was not in the centre of the display
• [Python/Matlab] Fixed the formula for computing display's pixels-per-degree for the fixation point different from the centre of the display
• [Python] Ability to add a custom fvvdp_display_geometry that varies ppd across the screen
• [Matlab] Minor bug fixes