Problems:
1. Can't get individual parts of a key-chord separately: modifiers, key.
2. Can't separate a key-combo into individual key-chords.
Solution:
Enhance `vim.keycode()` to optionally return a structured parse result
as a list of key-chords:
- `key_raw` the key-chord (problem 2)
- `mod` the modifiers of `key_raw` (problem 1)
- `key_orig` the key part of the key-chord, only here if differing from `key`
(this doesn't solve any of the above mentioned problems, but it may provide
useful and it's (in terms of code) free)
- `key` a normalized version of `key_orig` (solving problem 1), example(the
first is `key_orig` and second is `key`): `lt` and `<`, `Bar` and `|` (in
`<C-Bar>`)
