sitename missing from makedocs docstring

[tpapp]

I think makedocs(sitename = ...) is still required, but is no longer mentioned at
https://juliadocs.github.io/Documenter.jl/dev/lib/public/

[mortenpi]

Hmm. It is required for the (default) HTML, used by LaTeX, but the build should finish if it is unset and completely unused by the Markdown output. We should either make it Writer-specific or mandatory for all writers -- not sure which is the better option though.

[tpapp]

Friendly bump --- until a decision is reached, would it make sense to mention sitename in the docstring of makedocs? It is still used and even tested for.

[fredrikekre]

Yea, please make a PR.