Properly support framework multi-targeting

[artiomchi]

At the moment, this is either ignored (best case), or no code will be identified by the compiler in the first place (worst case!)

When R4Mvc.Tools loads a web project, we have to identify the target framework of that project, and possibly configure MSBuild to pick a desired framework. Need to test that with multi targeted projects, as well as identifying the differences based on which framework comes first in that list.

[artiomchi]

So, there's no perfect solution for this just yet, but I just came up with a pretty decent workaround that will let people use R4Mvc in their multi-targeted projects!

To do this, you'll have to change your csproj file to only use one framework when the project is built by R4Mvc using a build property, like follows:

<PropertyGroup Condition="$(IsR4MvcBuild) == ''">
  <TargetFrameworks>net462;netcoreapp2.1</TargetFrameworks>
</PropertyGroup>

<PropertyGroup Condition="$(IsR4MvcBuild) != ''">
  <TargetFramework>netcoreapp2.1</TargetFramework>
</PropertyGroup>

Your regular builds won't be affected, but R4Mvc will be able to handle it just fine.

Can't come up with a proper fix yet, as MSBuild seems to have some issues that doesn't make it easy to load multi-targeted projects (with dependencies that target other frameworks). I'll still keep an eye on this, and hopefully will eventually find a proper solution to this.

Buildalyzer is actually a great option as well, but at the moment it doesn't work either (thanks to a different issue with MSBuild!)

Until then, I'll leave this issue open. If anyone has an even better solution to this - help is always greatly appreciated!

[artiomchi]

Moving this to v1 Backlog, since we now have a workaround in place, which makes the current library usable in multi targeted projects