This commit restructures many of the ES6 modules, splitting them
up to actual export multiple functions instead of a single object.
It also splits up Util into multiple sub-modules, to make it easier
to maintain.
Finally, localisation is renamed to localization.
This removes the special comment part of the ES6 module syntax,
opting to enable ES6 module syntax by default.
It also appends `.js` to all import paths to better support in-browser
loading.
This commit moves all the input-related files from `core/`
to `core/input/`, and renames a couple as relevant
(input.js --> input/devices.js, keyboard.js --> input/util.js).
Pierre Ossman
Solly Ross
Asad Saeed