Add readline keybindings to read function

[SquidDev]

This adds a selection of keybindings to the read function which mirror those provided by readline (shell command prompts, several REPLs, etc...). I'm not entirely sure whether this should actually be included - it does bloat the already large bios.lua. However it does make inputting long text (especially in the lua program) slightly easier. I guess you can make up your mind for yourself 😄.

Keybindings

This provides the most basic keybindings as given here.

• C-a / C-e to jump to beginning/end of line
• C-d to exit read without inputting anything. This could cause problems as read can now return nil. However, it does mean you can exit lua and shell without having to type an explicit "exit".
• C-b / C-f to move left/right one character
• M-b / M-f to move left/right one word.
• C-p / C-n to move backwards/forwards in history or completions.
• C-u / C-k to delete to the beginning/end of line.
• C-w / M-d to delete to the beginning of the previous word/end of next word. (Note, the docs say it should be M-DEL rather than C-w. However, most of the things I've experimented with use the latter).

This doesn't define any of the more complex command like undo, transpose, yanking, etc... I'm happy to add them if people really want them, but it feels rather overkill.

Implementation

I'm currently listening to key_down/key_up events to track the status of control/alt keys. This is fine most of the time, though could cause problems with multiple users or people exiting the GUI with keys down. A couple of changes which could be made elsewhere to fix this:

• Trigger key_up events when the terminal is closed.
• Include modifier keys in the key event. I'm not a fan of this as it seems too "friendly" for the user, but it is the most fool-proof way.

Possible extensions

It might be nice to add similar shortcuts to edit. A similar system could also be added to the pager described in #212. I'd be happy to add them if people want.

[dan200]

Not a fan of these, sorry. CraftOS is not unix!

[SquidDev]

That's fine, I wasn't too sure about it myself 😄.. I don't there is an equivalent set of key bindings you'd consider using instead? For instance Ctrl+Left/Right to jump forwards/backwards words?