Figure out a way to handle whitespaces more strictly

[tohrnii]

Currently, the following statements are equivalent:

let x = a[0]

let x = a   [0]

and

let x = a
[0]

Ideally, only the first one should be valid.

Originally proposed by @bobbinth in #123 (comment)

[bobbinth]

Maybe we can just add semi-colons to address this.

[bobbinth]

Largely closed by #353. The only outstanding thing is adding commas to separate arms of the match statement.

sydhds will open a PR for this soon.