Introduce BenchmarkDotNet.Annotations

[AndreyAkinshin]

We should move all API which includes attributes and configs to a separate NuGet package BenchmarkDotNet.Annotations.
Benefits:

• This package can target .NETStandard 1.0, so it will be possible to declare benchmarks in .NETStandard projects
• We should be able to run benchmarks from such projects not only managed API (BenchmarkRunner.Run), but also via command line (like dotnet benchmark, see Add a "benchmark" cmd to dotnet #213)
• It will be possible to implement adapters for other benchmark attribute systems (like xunit-performance)

[AndreyAkinshin]

@adamsitnik, what do you think about this idea?

[adamsitnik]

I really like this idea! It looks like it's a must-have for some scenarios like "I have this piece of IL, please just run it for framework X".

[adamsitnik]

@AndreyAkinshin can I take this issue? it's blocking me

moreover, I have an additional idea: maybe we keep all the types from BenchmarkDotNet.Annotations in a flat BenchmarkDotNet namespace? So when the user puts using BenchmarkDotNet in the code file it's possible to use all our features OOTB without forgetting about the extra Alt+Enter/Ctrl+. to add all the includes? I know it's a breaking change, but I think that our users would like it.

[AndreyAkinshin]

can I take this issue? it's blocking me

Sure.

[AndreyAkinshin]

@adamsitnik, I think, it makes sense to release it in v0.11.x because it contains some breaking changes (with a few other things which also contain breaking changes; I will create corresponding changes soon).

[AndreyAkinshin]

moreover, I have an additional idea: maybe we keep all the types from BenchmarkDotNet.Annotations in a flat BenchmarkDotNet namespace?

Yes, it's a very good idea, I like it!

[Mike-E-angelo]

Is this available on a preview feed somewhere, by chance? Now that I am able to code again (😄) I was looking into creating a .NET Standard library with Benchmark.NET-specific classes. For instance, a strongly-typed wrapper around EnvironmentVariable so that I can keep from having to rely on different text strings for variable names (and values, for that matter).

[adamsitnik]

@mike-eee our preview package targets .NET Standard 2.0, you can get if from:

<packageSources>
  <add key="bdn-nightly" value="https://ci.appveyor.com/nuget/benchmarkdotnet" />
</packageSources>

[Mike-E-angelo]

Beautimous. Thank you, @adamsitnik. 👍

[WojciechNagorski]

@adamsitnik Can I help with this issue or is it already done?
After that I could help in #213