Adopt .NET naming and structure: CsMic.* namespaces, PascalCase projects and solution; update Coco namespace; update package id and NuGet publish target; adjust project refs and tests.

src/StandardLibrary/functions/Sign.cs

@@ -0,0 +1,38 @@
+using CsMic;
+using FunctionValueType = CsMic.FunctionValueType;
+
+namespace CsMic.StandardLibrary.Functions
+{
+    public class Sign : FunctionBase, ICodedFunction
+    {
+        public const decimal POSITIVE = 1;
+        public const decimal NEGATIVE = -1;
+
+        public string Name
+        {
+            get
+            {
+                return "sign";
+            }
+        }
+
+        public override IEnumerable<FunctionArgument> ExpectedArguments
+        {
+            get
+            {
+                yield return new FunctionArgument("value", FunctionValue.NUMBER);
+            }
+        }
+
+        public FunctionValue Execute(params FunctionArgument[] args)
+        {
+            return base.Execute(args, (_args) =>
+            {
+                var input = _args[0].Value;
+                decimal number = Convert.ToDecimal(input.Value);
+
+                return new FunctionValue(FunctionValueType.Numeric, number >= 0 ? POSITIVE : NEGATIVE);
+            });
+        }
+    }
+}