Redirect old docs to new docs

[kylebeggs]

The docs show an example for constructing a PolyArea here, which no longer works. I made an issue instead of just submitting a PR to fix the docs to make sure this was intentional.

[juliohm]

The docs are now hosted at MeshDocs. We should redirect the link above to the new site.

Documenter's maintainers added a function for this redirection recently, but we didn't have time to try it:

JuliaDocs/DocumenterTools.jl#76

Any help creating this redirection would be great.

[juliohm]

You can access the new docs with the badges on the README.

[kylebeggs]

Ok, I see. That would explain it as I usually just google search for the docs page.

[eliascarv]

Resolved in 4ddb1a0