Switch back from project.json and xproj to csproj, support dotnet cli preview 3

[AndreyAkinshin]

@adamsitnik, it's time to get rid of the project.json files!

[adamsitnik]

I definitely plan to implement this, but currently there are few blocking issues:

1. It works only with Visual Studio 2017 which is still RC, no support for VS 2015.
2. Moving from xprojs to csprojs is something new, probably easy to do, the thing is that I will need to rewrite our Core Toolchain once again. This might be tricky and time consuming.

I would like to wait a little bit (at least few weeks) to see if our "main" .NET Core users will move to csprojs to see if anybody needs that.

[adamsitnik]

Results of my twitter form with 421 answers:

[adamsitnik]

@AndreyAkinshin there is one good thing. Roslyn is cross platform now, so I will try to have a single Toolchain for both classic and Core .NET ;) There is a chance that we will not need a strong dependency to dotnet cli anymore ;)

[AndreyAkinshin]

Sounds great!

[mattwarren]

I think it's amazing that there are over 400 people who like BenchamrkDotNet enough (and presumably use it), to vote in a Twitter poll, that's fantastic!!!

[adamsitnik]

@mattwarren I was surprised too! I got so many answers mostly because Ben and then @dotnet have retweeted my tweet ;)

[bojanrajkovic]

This would be nice to have sooner rather than later. I was able to run the generated project.json-based code by using dotnet migrate and some manual hackery of both the project.json and generated .csproj, but of course, that didn't give me nice output. :)

[roji]

+1 on this, since updating my project to the new csproj format I can no longer run benchmarks... I really hope you guys get around to doing this soon!