Vertices

*** Please do NOT merge ***

- I'd like to freeze HEAD until 1.2 is uploaded.

- I want to see what others think of this definition of Vertex

The idea is that Trails and Paths only have vertices in between segments if the derivative (slope) changes.
That way for example a hexagon has 6 vertices, but a circle has none. Unlike the current implementation where a circle has 4 vertices. The an objects vertices should not depend on its implementation, see the trello card about getting rid of `decorateFoo`. I think that the semantics implemented here makes sense since segments (lines and beziers) are always differentialbe, the only place we can have a vertex is at a connection, hence it suffices to check the slopes at the connections.