Added support for running C# code in a dotnet core environment

environments/dotnet/FissionCompiler.cs

@@ -0,0 +1,59 @@
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Reflection;
+using System.Runtime.Loader;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp;
+using Microsoft.CodeAnalysis.Emit;
+
+namespace Fission.DotNetCore.Compiler
+{
+    //adapted from this article http://www.tugberkugurlu.com/archive/compiling-c-sharp-code-into-memory-and-executing-it-with-roslyn
+    class FissionCompiler
+    {
+        public static Function Compile(string code, out List<string> errors) {
+            errors = new List<string>();
+
+            SyntaxTree syntaxTree = CSharpSyntaxTree.ParseText(code);
+            
+            string assemblyName = Path.GetRandomFileName();
+            MetadataReference[] references = new MetadataReference[]
+            {
+                MetadataReference.CreateFromFile(typeof(object).GetTypeInfo().Assembly.Location)
+            };
+            CSharpCompilation compilation = CSharpCompilation.Create(
+                assemblyName,
+                syntaxTrees: new[] { syntaxTree },
+                references: references,
+                options: new CSharpCompilationOptions(OutputKind.DynamicallyLinkedLibrary));
+    
+            using (var ms = new MemoryStream())
+            {
+                EmitResult result = compilation.Emit(ms);
+
+                if (!result.Success)
+                {
+                    IEnumerable<Diagnostic> failures = result.Diagnostics.Where(diagnostic => 
+                        diagnostic.IsWarningAsError || 
+                        diagnostic.Severity == DiagnosticSeverity.Error);
+
+                    foreach (Diagnostic diagnostic in failures)
+                    {
+                        errors.Add($"{diagnostic.Id}: {diagnostic.GetMessage()}");
+                    }
+                }
+                else
+                {
+                    ms.Seek(0, SeekOrigin.Begin);
+                    
+                    Assembly assembly = AssemblyLoadContext.Default.LoadFromStream(ms);
+                    var type = assembly.GetType("Fission");
+                    var info = type.GetMember("Run").First() as MethodInfo;
+                    return new Function(info);
+                }
+            }
+            return null;
+        }
+    }
+}