Don't blindly eat tokens when trying to match destructuring assignments

[50Wliu]

Fixes #57

I also took the liberty of rescoping some things (for example, { is clearly not a keyword.operator).

This regex might be able to be cleaned up a bit more...I would do the following, but I'm not sure if everything that would match is valid:

'begin': '(?<=\\s|^)({)(?=(.+?)}\\s+=)'
  'beginCaptures':
    '1':
      'name': 'punctuation.definition.destructuring.begin.bracket.curly.coffee'
    '2':
      'patterns': [
        {
          # move the patterns down below up here and get rid of those
        }
      ]

Some advice from someone who's more seasoned with Coffeescript would be nice.