Remove documentation page for v0.1

[jlumpe]

The v0.1 version of the documentation is the first result in a Google search for "docstringextensions" and the the third result for "docstringextensions.jl". This is very confusing because that page is not labeled with the version number and does not contain links to any of the other versions (was created with MkDocs, not Documenter.jl), which could lead users to believe it is for the most recent version. It might be a good idea to remove it from gh-pages or at least rebuild it with Documenter.jl.