Rebindable keyboard controls

[epozzobon]

This pull request makes it possible to rebind the keyboard controls in the xenia config file. This fixes #1333.
It supports switching layers using caps lock (as the current default key bindings) and multiple keys for the same gamepad input.

I acknowledge that the syntax is a bit awkward, and I would be happy to get some feedback on how I can improve it while maintaining compatibility with xenia's current key bindings.

As it stands, the syntax works like this:
keybind_a = "0xBA" # binds key code 0xBA to the A button
keybind_b = "'X'" # binds the X key to the B button. Chars are indicated by ' as per C convention.
keybind_a = "0xBA" # binds key code 0xBA to the A button
keybind_right_trigger = "'E' 'O'" # binds both keys E and O to the right trigger. Space is used as a separator.

Bind the S key to dpad down when caps lock or shift are enabled, and to left thumb down otherwise: (notice ^ and _ preceding the char/keycode)

keybind_dpad_down = "^'S'" 
keybind_left_thumb_down = "_'S'"

[gibbed]

In general, I like what you've done with the token stuff.

I don't really like the single quotes for character key definitions, but I haven't really thought of a better format yet. I'll think on it.

[gibbed]

Additionally, I will look at implementing support for TOML arrays in our config reader/writer so we can have that without having a custom thing just for keybinds.

[epozzobon]

All the issues you pointed out should now be fixed.
I also thought about a better syntax for the bindings: single quotations could be removed entirely, and instead all bindings are considered ascii by default except when they start with 0x.

I think it would make them look quite natural:
keybind_a = "0xBA" # binds key code 0xBA (VK_OEM_1) to the A button
keybind_b = "X" # binds the X key to the B button.
keybind_right_trigger = "E O" # binds both keys E and O to the right trigger. Space is used as a separator.

Bind the S key to dpad down when caps lock or shift are enabled, and to left thumb down otherwise: (notice ^ and _ preceding the char/keycode)

keybind_dpad_down = "^S" 
keybind_left_thumb_down = "_S"

[epozzobon]

(xb format makes a mess out of DEFINE_string statements so I'm not able to fix the continuous integration check.)

[gibbed]

You can selectively toggle off and on clang-format.

Surround it with:

// clang-format off

// clang-format on

[epozzobon]

I must be doing something wrong, but even with those lines, xb format tries to tab the entire namespace

[epozzobon]

Can this get merged or is any other change necessary?