Add `Direction::angle` method about hexx HOT 2 CLOSED

/// Returns the angle associated with the provided hex [`Direction`].
///
/// Measured in radians counterclockwise from the +x axis.
pub fn angle(direction: Direction) -> f32 {
    use Direction::*;
    // See https://dr282zn36sxxg.cloudfront.net/datastreams/f-d%3Adff233ddd1e7e4c34a6545a8dfc1d63bbaf7eefbb40215febc633a30%2BIMAGE_TINY%2BIMAGE_TINY.1
    PI / 6.
        * match direction {
            BottomRight => 11.,
            TopRight => 1.,
            Top => 3.,
            TopLeft => 5.,
            BottomLeft => 7.,
            Bottom => 9.,
        }
}

let layout = HexLayout::default();
let angle = layout.direction_angle(Direction::BottomRight);

let orientation = HexOrientation::pointy();
let angle = orientation.direction_angle(Direction::BottomRight);

let orientation = HexOrientation::pointy();
let angle = Direction::BottomRight.angle(&orientation);