Support more shortcuts

[dlee]

Support these additional shortcuts:

• alt-left (go to beginning of word)
• alt-right (go to end of word)
• ctrl-w / alt-backspace (rub-out to beginning of word like ctrl-backspace)
• ctrl-u (delete all text before cursor)

Note that alt-right should go to end of word, and not the beginning of next word (current ctrl-right behavior).