Move appendChild and attribute logic into files here #33
Description
Currently the same logic exists across yo-yoify and bel. It would be nice if it could be more shared and driven by this library.
It also means an element created with a specific version of bel may not be compatible with a specific version of yo-yoify. So yo-yoify should really require('bel/appendChild') and require('bel/attrs') from the local element it is transforming to ensure compatibility.