Add some emacs keybindings. Fixes #371

Add the most commonly used emacs/readline keybindings to input field and
document them.
Also change the wording on some of the old descritions to clarify
intent.
:+1:  on alt text, but I didn't want to explain them all as separate list elements, it's not our job to educe people on emacs keybindings, but alt-title is nonintrusive