add list of cases for manual testing

[slingamn]

We've accumulated a lot of cases that are likely to break:

1. Async output (use the async command in readline-demo)
2. History search done redraw issue #38
3. (Windows special cases?)

[slingamn]

In my first draft of #38 I apparently failed to test basic line editing functionality (moving backwards in the line, editing it, and having the buffer redraw correctly) :-|

[slingamn]

Text on the same line as the prompt should not be erased.

[wader]

I wonder what options there are to automate these kind of tests. I use a little bit of expect for testing some basic REPL stuff for fq but it has turned out quite hard to make the tests stable. Think i did look a bit at using https://github.com/charmbracelet/vhs but don't remember why i gave up on it. But those kind of tests wont really help testing for different platforms :(

[slingamn]

Alt-Arrow cases as in #59