Fix markdown bullet points in function docs

[frewsxcv]

Markdown requires a newline before bullet points, and since there's not one here, they'll get rendered incorrectly

[rust-highfive]

r? @alexcrichton

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[alexcrichton]

@bors: r+ rollup @everyone, would the above be a good alternative?

[bors]

@bors r=alexcrichton d6492e2

[alexcrichton]

oops

[alexcrichton]

@bors: r+ d6492e2