Support images to some extent on Windows

[mfontanini]

This PR attempts to add some support for images on Windows. Specifically:

• Getting the terminal size in pixels fails in that platform so instead we default to a 16 pixel font size and let you specify some other via the config file. This ain't great but it gets the job done.
• WezTerm seems to completely break if you hide the cursor and then display images on Windows (works fine in Linux!). So in that specific combo we don't hide the cursor. This is done only in that scenario as not hiding the cursor is suboptimal as you can sometimes see it moving, especially when printing images. Unfortunately without this images are completely broken there so this is better than nothing.

There's still more work to be done here. e.g. this doesn't work well in the git bash for windows terminal (whatever that is) but at least it seems to work on wezterm.

Relates to #13