Release v0.2.8

Changes

• Added extend() methods to add a component to a vector

let a = Vec2::new(0.0, 1.0);
let b = a.extend(2.0);

assert_eq!(b, Vec3::new(0.0, 1.0, 2.0));

• Added the swizzle feature which allows swizzling vector values

let a = Vec2::new(1.0, 2.0);
let b = a.xxyy();

assert_eq!(b, Vec4::new(1.0, 1.0, 2.0, 2.0));