x11/swayimg: add new port
Now you can view images directly in the current terminal window!
The program uses Sway IPC to determine the geometry of the currently
focused container. This data is used to calculate the position and
size of the new "overlay" window that will be used to draw the image.
In the next step, swayimg adds two Sway rules for the self window:
"floating enable" and "move position". Then it creates a new Wayland
window and draws the image from the specified file.