Add "waypoints" to the specification

[uo265363]

Adding "waypoints" optionally as a list of points with latitude, longitude, name and description.

[uo265363]

I think elevation should be added as an optional property instead of being a mandatory one, since it's redundant, google maps can get the elevation from the latitude and longitude.

[luispc1998]

I'll add them to the specification, elevation will appear in the examples. I'll take the schema.org property since it fits what we want, its type will xsd:double.