Consider changing from `?<number>` to `<C-<number>>`

[nullromo]

Ctrl+number is a lot easier to press than ?<number>. However, I need to check if Vim already uses <C-1>, etc.

[nullromo]

There should be an option of "leader mode" where a key is required first (like the ? key behavior right now) and also a key map mode where it's just a keymap. The Cash.nvim leader key should be customizable, as should the keymap mode. The default keymap mode mappings would be <C-1>, <C-2>, etc. but each of the 9 cash registers should have it's own unique key mapping.

[nullromo]

Closed #7 as a duplicate of this.

[nullromo]

The function keys (F1-F9) will work best.

Reference:

for f = 1, 12 do
    vim.keymap.set('n', '<F' .. f .. '>', function()
        vim.notify('F' .. f .. ' pressed')
    end, { desc = 'F' .. f .. ' key' })
end