Add key binding to skip the current word

[1ec5]

Tapping Shift before the start of a word causes Mudim to ignore just that word. This accelerator is useful for typing foreign words, and indeed I think Shift was chosen because these foreign words would tend to be proper nouns. But I don’t think Shift would be a good accelerator key, because it’s too easy to hit by accident: the user could have originally intended to capitalize a word but changed their mind. Perhaps Ctrl+Shift or LeftShift+RightShift would signal the intention better.