Shorthand snippet() to s()#154

Make a shorthand alias of snippet() so can type just s()

I am closing this as we won’t add a lot more global helper functions due to the potential for conflicts with other libraries. On top, we don’t see such shortcuts as advisable as they are hard to understand. And since Kirby easily allows anybody to define such helper functions for their own projects, I think that’s the best to do when one really needs one in their projects.