WIP: add keyup/down bind support

[bovine3dom]

I hate rebasing

Supercedes #1645

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Observations:

• implicit keyups aren't being ignored, j leads to scrolling twice
• hint mode broken
• user binds broken (e.g. :bind ,q fillcmdline test)
• sometimes follows links in hint modes(!?)
• adding a user bind of <D-j> binds to <<UD?-<>D<U?-D>-<U?-->j<U?-j>> (i.e. the key sequence literally typed out)
• hardcoded bind of <D-e> doesn't work

[bovine3dom]

I think I need to look back through #4440 and make sure that everywhere that changed things, keyup/keydown/repeat/optional key events work.

I also need to look back at #1645 and try to remember what it was I had decided about repeat keys - there is a .repeat property on keyboard events, maybe we need to update minimalKeyboardEvent to include that information?

I think I just deleted some logic about repeat that I probably shouldn't have deleted...