`p[q]`            0
`p + q`          +0.5
`p / q`          +1
`p.join(q)`      -1
`p.pathjoin(q)`  -1
`p.pathjoin(q)`  -1
`p.add(q)`       +0.5

Joining/adding/appending paths is one of the most common ops. Please let's make it short, easy and obvious.