Expand paths

[jonthegeek]

It's valid to give paths as relative to the base path where the doc is found. Sort that out.

Note: If the API's URL is apis.guru, we need to consult a special field for this.

[jonthegeek]

Still to-do (I think): Add a function that takes a rapid and returns a rapid, using @info@origin@url to expand `@servers@url. I don't THINK I can do it during creation, since props don't talk to one another that way.

Optionally I could make getters that do it on-demand. That might be the best option. Hmm.

[jonthegeek]

Getters would be really tricky. Let's make a function, can make it fancier later.