Migrate to csproj

[Tyrrrz]

I'm using this library in an app that runs inside a docker container. Due to having been built with project.json format, this library requires an sdk image to run, which is significantly bigger than the runtime image. Switching to csproj should fix it.

[omar]

Hey @Tyrrrz, this will be solved in the 2.0 release (see v2.0.0-alpha). That version is built for .NET Standard and uses .csproj.

It seems to be pretty stable at the moment and I'm hoping to promote it to stable v2 after I finish reviewing comments on #24.

[Tyrrrz]

I'm not really interested in the metric changes in 2.0 and I would like this fix as soon as possible. I can make a PR with just this change, would you merge it?

[Tyrrrz]

Also I would need to use this library in a project targeting net45 (outside of docker)