Add math.atan2

[gordonbondon]

No description provided.

[bioball]

Since we're linking to Wikipedia, let's use verbiage that aligns with it.

Also, need a @Since annotation.

Suggested change

	/// Returns the [4-quadrant inverse tangent][1] of [x] and [y].
	///
	/// [1]: https://en.wikipedia.org/wiki/Atan2
	/// Returns the [2-argument arctangent][1] of [x] and [y].
	///
	/// [1]: https://en.wikipedia.org/wiki/Atan2
	@Since { version = "0.28.0" }

It might also be helpful to have one more paragraph to describe this function's purpose. Maybe something like: "The result is 𝜃 (theta) when converting cartesian coordinates 𝑥 and 𝑦 to polar coordinates 𝑟 and 𝜃."

[holzensp]

Needs a confirmation approval from @bioball (having requested changes); they look addressed to me.

[bioball]

LGTM!