This change updates the StartVS script in the following ways:
* Ported batch file to a PowerShell script. The batch file is still
there. It just runs the PowerShell script.
* Added a `-chooseVS` switch that displays a menu of Visual Studio
instances that are installed and allows the user to pick one to
launch.
* Added an `-includeRoslynDeps` switch that sets an environment variable
that controls whether Roslyn dependencies are included with the
Razor extension or not.
Since integrating our repos, there have been a number of changes in PRs that touch the encoding of the file, adding or removing a BOM as the editor in question decides. I've standardized on UTF-8 with BOM, as we do in roslyn, and put it in the .gitattributes so it should hopefully stay consistent.
* Remove razor-compiler.sln from root directory
* Move Razor.sln and Razor.Slim.slnf into root directory
* Put all projects from razor-compiler.sln into Razor.sln, with same solution folder layout
* Fix builds and docs
* Remove a couple of redundant files in the src\Razor folder
@ryanbrandenburg pointed out my change from `. .\activate.ps1` to `.\activate.ps1` in the build from source PR. I've been `.\activate.ps1` and haven't run into any particular issues, however, it's not the recommended way to source due to [scoping](https://docs.microsoft.com/powershell/module/microsoft.powershell.core/about/about_scripts#script-scope-and-dot-sourcing). dotnet/aspnetcore enforces this dot sourcing, so I copied over the script changes here.
Also noticed startvs.cmd had changed so brought that over as well.
Dustin Campbell
Fred Silberberg
David Wengier
Ryan Brandenburg
Tanay Parikh
Nate McMaster
Brice Lambson