Adds a few things to our vec impls:

• Aliases for the Processing4 names. I disagree strongly with some of these names but am going to make them available to assist porting sketches. I think aliases are fine and we can make a final decision (either to alias, make canonical, or remove later).
• Adds some more functional methods like truncate and extend that are necessary in order to go from Vec2 to Vec3, etc.
• Adds swizzles! These are dispatched dynamically and also allow easily changing dimensions, e.g. vec2.xxyy, etc.