VS loves to screw around with the csproj format, so move all the custom rules
into separate files that it can't screw around with.

This also gives the added benefit of shutting up the warning about duplicate
AssemblyVersionInformation types, because apparently VS doesn't show files
that are included for compilation from external targets files but it still
includes them in the compilation (bug? feature? shrug)

Add instructions for the GitHub.Unity.OctokitDebugging solution

Add mono-built versions of octokit and dotnet-http.
Octokit: 0.23.0.1
dotnet-httpClient35: 3.5.0.0 (3.5.22000.1-gfu)