Between = function (x1, y1, x2, y2)
{
    return Math.atan2(y2 - y1, x2 - x1);
}
Find the angle of a segment from (x1, y1) -> (x2, y2).

@function Phaser.Math.Angle.Between
@since 3.0.0

@param {number} x1 - The x coordinate of the first point.
@param {number} y1 - The y coordinate of the first point.
@param {number} x2 - The x coordinate of the second point.
@param {number} y2 - The y coordinate of the second point.

@return {number} The angle in radians.