allow running doctests with Revise

[simeonschaub]

I think it would be quite useful to be able to run doctests using Revise as well. This worked for me locally, but please let me know if this should be implemented in a different way. Right now, I am creating a new environment in doc/deps/revise, in which Revise is installed and then I push that onto LOAD_PATH, but there might be a nicer way to do this.

[staticfloat]

I don't think I'm the right person to review this. Maybe @fredrikekre? :)

[StefanKarpinski]

@Keno might be a good person to review since he added the revise-test functionality.

[simeonschaub]

Just bumping this again. Not really urgent, but I think this would be nice to have.

[timholy]

I like it!

Maybe it's just me, but I use "draft" to mean "something I am working on that isn't ready for review yet". So I never review anything marked "draft" unless specifically requested.

[fingolfin]

This seems suuuuper helpful. I must confessed that I've given up on more than one doc change PR for Julia because the "modify - rebuild Julia - fix mistake - rebuild Julia - ... " cycle is sooo painful (I was trying to add more crossrefs and examples, and just figuring out how to get the crossrefs working drove me crazy and I gave up).

I can only speak for myself, but I think this PR would substantially boost my motivation to contribute tweaks to the Julia documentation, and hopefully it would do so for others, too.

[simeonschaub]

I just started looking into this again, but doesn't seem like this works for Base yet and it also automatically rebuilds Julia every time changes are made to Base, so marking this as a draft again until I figure this out.

[simeonschaub]

Ok, I now tested this locally for Base and LinearAlgebra and everything seemed to work as expected.