Teach plover about the {calc} key: how to format it
Add calculator button to dict.json by default
Include keycodes in Windows KeyboardEvents

Before this change, windows events didn't have
the keycode member variable. I've added it in
here, and also forwarded unrecognized
characters so I can catch the keycodes later.
Add f23 and f24 keys to sidewinder code and dictionary

Some default keys to turn Plover on and off. May not
work well for a sidewinder, but is ideal for an
Ergodox with access to arbitrary keycodes.

Shows a good jumping-off point for others interested in
using non-printing toggle keys.
Add DebugView logging to keyboard handler
and additional debug output to facilitate
debugging of suspected 'stuck keys' issue.
Strip other keycodes from an F24 keypress.
Lengthening undo buffer