Demonstrate new features in FSharp.Formatting

I upgrade FSharp.Formatting to version 2.3.5-beta which uses more up-to-date backend, `FSharp.Compiler.Service`.

Two new features have been shown in generating API docs:

 - Generate links to GitHub source of all functions and members. See detailed description at http://tpetricek.github.io/FSharp.Formatting/metadata.html.
 - Filter to display only public members in documentation.

This would provide better default API doc generation usage.

This is resulted from brief discussion at https://github.com/tpetricek/FSharp.Formatting/pull/81#issuecomment-32830684

cc @forki