add intersphinx, and modify a few blurbs to make use of it

[jakkdl]

I didn't bother a more comprehensive rewrite of blurbs, since a lot are getting rewritten in #248. Only changed a few to make sure that the intersphinx links worked.

[jakkdl]

...no RTD build in the checks??

edit: nvm it showed up and looks good.

[Zac-HD]

...no RTD build in the checks??

I went and marked this as a required check, so we'll block on it in future 🙂