Allow to compile a cs files without a project

[shargon]

I think that we can download the package if the user want to compile a single file, and use the source included in the package for this compilation

neo-devpack-dotnet/src/Neo.Compiler.CSharp/CompilationEngine.cs

Line 67 in 7add5a9

MetadataReference.CreateFromFile(typeof(scfx.Neo.SmartContract.Framework.SmartContract).Assembly.Location)

https://github.com/dotnet/docs/blob/main/docs%2Fcore%2Ftools%2Fdotnet-tool-install.md