ISO third level keys were not working. That prevented some inputting
important characters (like pipe `|` and caret `^`) on some keyboard
layouts.
Instead of parsing the user-agent string to find the users os, we now
look into the `platform` attribute of the `navigator` object.
Removed the hijacking of the command key `⌘` on Mac OS as the `Alt` key
on other systems.
runarberg
Paris
Daniel Imms
Christopher Jeffrey