Port to .NET Standard

[mikecousins]

Any chance you're planning on porting this to .NET Standard?

[mikecousins]

I have added pull request #3 which is one of the first steps in the port if you want to help out.

[BrendanGrant]

You can find a version that does that here: https://github.com/BrendanGrant/NSpeedTestStandard