Check CI for "build -t All" for mac (linux and windows outstanding)

[dsyme]

This attempts to get the build working up to

dotnet fake build -t All

It is trying Windows first

The build on Ubuntu is failing with R packages not being found by the type provider. Not clear why, see #213

[AndrewIOM]

On my local branch I managed to get macOS working similar to the good progress by @nhirschey in #216.

I hit issues with other platforms to do with R environment configuration - there was an overlooked macos hardcoded path so this has been reconfigured to be set dynamically based on platform when starting the RProvider server.

There is an outstanding issue with running FAKE's All target on other platforms - the test project hangs forever, and requires further investigation. Nuget deployment, version tagging / release etc. is also still outstanding.

Documentation deployment is working with the macos CI setup (currently no windows or ubuntu). I'm going to merge this PR and suggest that we continue work to get all platforms working in #216 .