Add support for using Ctrl/Alt/Meta with non-character keys

[dubrowgn]

Currently, key modifiers can only be used in conjunction with keys which map to a printable character. This pull request is a refactor that allows key modifiers to be used with any key, such as arrow keys, tab, etc.

[gwenn]

I agree that ctrl-left/up/right/down, shift-left/up/right/down are missing.
But I am not sure that your PR is the right approach.
Because it is possible to do ctrl-alt-shift-left.
Maybe we should do something similar to Haskeline ?

[dubrowgn]

It's a good point. What do you think of something like this then?

pub enum Key {
    Backspace,
    Char(char),
    Delete,
    Down,
    End,
    Enter,
    Esc,
    Home,
    Insert,
    Left,
    Null,
    PageDown,
    PageUp,
    Right,
    Tab,
    Unknown, // not sure about this, from UnknownEscSeq
    Up,
}

pub struct KeyPress {
    pub key: Key,
    pub ctrl: bool,
    pub alt: bool,
    pub shift: bool,
    pub meta: bool,
}

[gwenn]

altand meta are the same by default on most unix keyboard, no ?
https://unix.stackexchange.com/questions/28993/what-is-bashs-meta-key:

By default, on most setups, the Meta key is the key labeled Alt. This is because historically, many unix workstations had a key labeled Meta where PCs have a key labeled Alt.

[dubrowgn]

In many other contexts the meta key is the same as the super key (aka windows, command, etc).

https://developer.mozilla.org/en-US/docs/Web/API/KeyboardEvent/metaKey
https://forum.kde.org/viewtopic.php?f=111&t=88599

For clarity, I suppose it would be better to call it super here, instead of meta.

[dubrowgn]

So, I'm playing around with this a bit. I ended up implementing the above proposal and several macro helpers. What do you think?

[gwenn]

I don't know if the pending PRs will be integrated one day and, if they are, in which order.
But your PR and #103 will generate a lot of conflicts.

[dubrowgn]

Indeed, although I suspect this PR will cause many conflicts with just about any other change. There is a lot being touched for this.

[gwenn]

Would you mind closing the PR ?