Feature: Sixel support

[swiftgeek]

Bunch of links:

• https://en.wikipedia.org/wiki/Sixel
• https://github.com/saitoha/PySixel
• https://github.com/saitoha/libsixel

Sixel support in kmscon could be a nice addition aiding effort of dropping CONFIG_VT while keeping some of its familiar features (from user perspective, like playing video with mpv on console), and potentially could be even paired with wayland compositor like weston as the worst possible fallback

I guess this applies more to libtsm