[Request] Add highlight for {!} formulae in visualforce

[YodaDaCoda]

I've mucked around a bit and adding the below to 'patterns': [ gives something reasonable, but I have no idea if it's appropriate.

{
  'name': 'support.function.formula.visualforce'
  'begin': '{!'
  'end': '}'
  'captures':
    '0':
      'name': 'support.function.formula.visualforce'
}