I've wanted to avoid checking in all the screenshot pics as the png
files change every time I run the generation script, and it bloats
the repo over time.
This commit changes the doc generation step to use the asciinema
web player with the equivalent contents.
Really, it's only a smallish step to go from this to just emitting
the html directly in the doc pages, but I think I might use
the player for some examples in the future.
I think this is still a fine step for now in any case.
While comparing this with the existing screenshots, I noticed the
the Alabaster screen shot png has the wrong color for its rightmost
column: there's an issue in wezterm in parsing the dynamic color
escapes that causes it to pick up the wrong color.
Loading the scheme by name has the correct color and matches
how it is shown as of this commit.
