Add æ and œ ligatures

[pelson]

Comment in #11 (#11 (comment))

It is difficult to distinguish "æ" from "œ". I want "open a"

[pelson]

Note that I've generated something with ChatGPT (@Carreau's prediction 😂):

This was using the prompt:

Take this image, and generate an image containing ẞ, ß, Æ, Œ, a, æ, œ, ð, Þ, þ characters in the same style. The a and æ should use double-story form.

Along with the original handwriting sample.

The only existing form that I could find anywhere in XKCD is https://xkcd.com/2763/ (Æ)

[pelson]

I prefer to use the XKCD form for the Æ.

[pelson]

The ð could be generated from an existing line + https://xkcd.com/2520/