Auto-transform reserved words to be quoted in non-es5 mode:

1. Class methods uses a computed member expression on the prototype when the method name is a reserved word
2. Destructering would use a computed member expression when the key to pull is a reserved word
3. Object concise method will qoute the identifier (i.e. make it a string literal) when it's a reserved words
4. reserved-word-visitor is a default visitor in non-es5 mode that would handles everything else:
  a. Handles properties in object expressions
  b. Handles member expressions
Meh -- seems pretty harmless to just always do this, right? (i.e. it's not like computed expressions are deprecated or pose any issues in ES5 code too -- so might as well just drop the option check and always quote them in the output)