Curtsies

- Fix accidentally quadratic `width_aware_slice` behavior (fixes bpython 729)
This bug causes bpython to hang on large output. Thanks Ben Wiederhake!
- Allow curtsies to be run on non-main threads (useful for bpython 555)
This should allow bpython to be run in a variety of situations like Django's runserver
- Add function keys for some keyboard/terminal setups

- Handle unsupported SGR codes (fixes bpython 657)
- Add Ctrl-Delete for some keyboard/terminal setups
- Many doc fixes. Thanks Dan Puttick!

- Add sequences for home and end (fixes Curtsies 78)

- Fix 90 again
- Strip ansi escape sequences if parsing fmtstr input fails
- Prevent invalid negative cursor positions in CursorAwareWindow (fixes bpython 607)
- '\x1bOA' changed from ctrl-arrow key to arrow key (fixes bpython 621)
- Alternate codes for F1-F4 (fixes bpython 626)