Remove Compat dependency and references to Pkg.dir

[ararslan]

Also require 0.7

The diff is big

[ararslan]

FYI this is needed fairly urgently to get 1.0 docs for Julia itself

[ararslan]

Actually only a small bit of this is required in order to deploy documentation, and we're doing that locally to get 1.0 docs. This will be needed for packages on 0.7/1.0 though.

[mortenpi]

Ok, this is a bit of a surprise. I somehow assumed that a 0.6-Compatted package would just work on 1.0. I'll merge and tag #782, and then we can deal with this next.

[fredrikekre]

@mortenpi it's chill, I built docs locally and pushed to gh pages for now so there is no rush.

[mortenpi]

This is not actually necessary for 0.7/1.0 deployments, right? Documenter should actually be working fine on 1.0 at the moment.

Pkg.dir does need to be fixed, but that only affects Travis.genkeys and generate, neither of which are important for doc builds.

[ararslan]

Documenter should actually be working fine on 1.0 at the moment.

Not for deployment, which is how we noticed that the package needed to be updated, and as you said, generation and Travis stuff.

[mortenpi]

The deprecation that failed the deployment was fixed in v0.19.3, but unfortunately Documenter hadn't been updated in Base. Ref: JuliaLang/julia#28559

[fredrikekre]

#795