simpler balloon encoding into image

[maandree]

Idea from: https://github.com/jaseg/pixelterm
$balloon20,5$ should be possible to encode as a 20×10 rectangle.

This makes it easy to draw even the balloon in the GIMP.

[maandree]

Untested and undocumentented.
Current status: Minimum width only supported and only supported for import.
Colour designation: argb(100, 0, 255, 0)

Goal: Support for minimum/maximum width/height.
Minimum colour: argb(100, 0, 255, 0)
Maximum colour: argb(100, 255, 255, 0)
As well as offset (left/top) support, with colour: argb(100, 0, 255, 255)

Justification could be encoded on the bottom left pixel:
Alpha xor:ed by 0x80 to toggle: Pony.Balloon.LEFT
Red xor:ed by 0x80 to toggle: Pony.Balloon.RIGHT
(LEFT | RIGHT = CENTRE)
Green xor:ed by 0x80 to toggle: Pony.Balloon.TOP
Bluee xor:ed by 0x80 to toggle: Pony.Balloon.BOTTOM
(TOP | BOTTOM → MIDDLE)