WIP: Enable Unidoc

[alexandru]

Trying to enable the unidoc plugin, unfortunately it fails currently.

I'm creating the PR, then opening an issue on unidoc's repo.

The error I'm seeing:

> unidoc
[info] Compiling 9 Scala sources to cats-effect/core/jvm/target/scala-2.12/classes...
[info] Main Scala API documentation to cats-effect/target/scala-2.12/unidoc...
[error] Symbol 'type cats.effect.Effect.ToEffectOps' is missing from the classpath.
[error] This symbol is required by 'package cats.effect.implicits.package'.
[error] Make sure that type ToEffectOps is in your classpath and check for conflicting dependencies with `-Ylog-classpath`.
[error] A full rebuild may help if 'package.class' was compiled against an incompatible version of cats.effect.Effect.
[info] No documentation generated with unsuccessful compiler run
[error] one error found
[error] (root/scalaunidoc:doc) Scaladoc generation failed
[error] Total time: 9 s, completed Apr 24, 2017 11:04:43 PM

I've opened the issue at: sbt/sbt-unidoc#35

[djspiewak]

Cool, ty. As a random methodology FYI, since this PR is marked as "WIP", I'm ok with rebasing at your discretion.

[alexandru]

I opened the issue on the sbt-unidoc issue tracker.

@djspiewak I think we should disable Xfatal-errors on normal doc and (assuming we enable Unidoc) to leave that on only for unidoc, which should run in Travis only for the "main" Scala version.

I already did that in this PR, which is why the Travis build is failing only for Scala 2.11:
https://travis-ci.org/typelevel/cats-effect/builds/225355929

[djspiewak]

@alexandru Disabling -Xfatal-errors for doc seems perfectly reasonable.

[rossabaker]

I've used and endorse that disabling.

[alexandru]

Status: I haven't figured out how to fix this and nobody responded yet on sbt/sbt-unidoc#35

[alexandru]

Haven't been able to make progress on this PR and there's no use in keeping it around, so closing it.