Create a LINQPad custom visualizer

[zspitz]

https://www.linqpad.net/CustomVisualizers.aspx

• Create a new project - LinqPad; multitarget .NET Core and Framework
• Reference ExpressionTreeVisualizer.UI NuGet package
• (ExpressionTreeVisualizer.Dev only) Add a build step to output to the LINQPad plugin folder
• Add a new ZIP file with the built DLL to Releases

Open questions:

• Dependent DLLs of the main DLL? https://forum.linqpad.net/discussion/2454/dependencies-of-custom-visualizers/p1
  See https://github.com/zspitz/Periscope.Debuggee/blob/master/SubfolderAssemblyResolver.cs
• Settings read/write?
• Dark theme?

[zspitz]

Related #114