add a row of little buttons for keys that aren't available on iOS/iPadOS for terminal

[williamstein]

• tab key for completion
• arrow keys for line editing/navigation
• control+c
• control+d
• escape

Without these, it's hard to even test out mobile safari functionality, and basically all of the value of readline is lost (e.g., history).

[williamstein]

Additional comment here -- one of the massive shortcomings of xterm.js is that it doesn't support copy/paste on iOS with any of the three renderes (DOM, Canvas, WebGL). It's predecessor term.js actually did. This also really should get fixed, and might just be some easy CSS tweak. Failing this, at least a little input box you can paste into would help a lot.

[williamstein]

I'm going to keep cowasm bare bones, and do any work like this as part of other projects (like cocalc). Cowasm is a lower level components.