Add "super-strict" mode - removing JS warts

[tehsenaus]

Things to disallow:

• == operator (type coercion)
• function declarations (allow expressions only)?
• block scope always - disallow var??

(http://ejohn.org/blog/javascript-as-a-first-language/)

• arguments (not an array, not needed anymore with rest-params?)
• modifying Object.prototype, Array.prototype (but allow non-enumerable properties)

(http://matt.might.net/articles/javascript-warts/)

• 'this'... can it be fixed?
  • remove it, require it to be declared as part of function params (special syntax)
  • with arrow functions, is it worth fixing?