Introduce TOML support to keymap file loading

[metalefty]

I started TOMLification starting from keymap files. I confirmed that TOML loader is valid by comparing structures loaded by both loaders are identical.

Things done in this PR:

• Put TOML keymap files converted from INI keymaps
• Implement TOML loader
• Test keymap structure loaded from INI and TOML are identical

Not done in this PR:

• Switch to TOML keymap loader completely
• Removing INI keymap loader and INI keymap files