Improve destructuring

[winstliu]

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There have been a few destructuring changes recently (#82, #104, #106) that I think have improved the general reliability of destructuring tokenization. However, there's still a few things I'd like to improve. Specifically:

• Tokenize destructuring in function parameters such as setWindowDimensions: ({x, y, width, height}) ->.
  There are two changes required for this one: getting rid of the beginning-of-line requirement as well as figuring out how to get rid of the equals sign requirement.
• Tokenize destructuring that occurs as a result of a return statement, either explicitly or implicitly (such as return {x, y, width, height, maximized} where the return is optional).
• Change the meta scope to not include variable.assignment to avoid confusing syntax themes.

This is mostly a reminder for me after #103 is merged, though if someone else wants to tackle these issues, that's fine by me!