* `App.modifier_down(key)` -- returns `true` if the given key (doesn't
  actually have to be just a modifier) is currently pressed.

* `App.key_down(key)` -- returns `true` if the given key is currently pressed.

  return App.modifier_down('lctrl') or App.modifier_down('rctrl')

  return App.key_down('lctrl') or App.key_down('rctrl')

  return App.modifier_down('lalt') or App.modifier_down('ralt')

  return App.key_down('lalt') or App.key_down('ralt')

  return App.modifier_down('lshift') or App.modifier_down('rshift')

  return App.key_down('lshift') or App.key_down('rshift')

  return App.modifier_down('lgui') or App.modifier_down('rgui')

  return App.key_down('lgui') or App.key_down('rgui')

function App.modifier_down(key)

function App.key_down(key)

  App.modifier_down = love.keyboard.isDown

  App.key_down = love.keyboard.isDown