`hex.publish` does not respect the docs output folder

[pnezis]

If you have set a different output folder for the docs in your project config then hex.publish will raise because it expects the docs to be under a doc or docs folder

 def project do
   [
     app: :my_app,
     version: "0.1.0",
     docs: [output: "another_path"]
   ]
 end

I can see two ways to address this:

• Accept an extra CLI option with the docs path, mix hex.publish --docs-path ....
• Use the output folder specified in the project's config if set

WDYT? Glad to send a PR.

[wojtekmach]

Good catch. --docs-path would be the most extensible way to go about it. Before doing that though I'm curious if we should go with something easier, i.e. mix hex.publish when publishing docs would look at Mix.Project.config()[:docs][:output] first. WDYT?

[pnezis]

Mix.Project.config()[:docs][:output] was also my first approach and I am fine going with this but:

• It introduces more coupling with ex_doc
• We should handle the case where :docs is a function instead of keyword list

[wojtekmach]

Good call, imho let's go with --docs-dir then. wdyt @ericmj @supersimple?

[ericmj]

I don't mind having defaults that match ex_doc since that's probably what 99%+ of mix+hex users are using. I think we should start by reading Mix.Project.config()[:docs] and if there is a need for --docs-dir we can add it later.