Add Runtime.Substring and Arrays.CopyOf

Antlr4.Runtime/Antlr4.Runtime.csproj

@@ -145,6 +145,8 @@
     <Compile Include="RecognitionException.cs" />
     <Compile Include="Recognizer`2.cs" />
     <Compile Include="RuleContext.cs" />
+    <Compile Include="Sharpen\Arrays.cs" />
+    <Compile Include="Sharpen\Runtime.cs" />
     <Compile Include="TokenStreamRewriter.cs" />
     <Compile Include="Tree\AbstractParseTreeVisitor`1.cs" />
     <Compile Include="Tree\ErrorNodeImpl.cs" />

Antlr4.Runtime/Sharpen/Arrays.cs

@@ -0,0 +1,13 @@
+namespace Sharpen
+{
+    using System;
+
+    internal static class Arrays
+    {
+        public static T[] CopyOf<T>(T[] array, int newSize)
+        {
+            Array.Resize(ref array, newSize);
+            return array;
+        }
+    }
+}

Antlr4.Runtime/Sharpen/Runtime.cs

@@ -0,0 +1,15 @@
+namespace Sharpen
+{
+    using System;
+
+    internal static class Runtime
+    {
+        public static string Substring(string str, int beginOffset, int endOffset)
+        {
+            if (str == null)
+                throw new ArgumentNullException("str");
+
+            return str.Substring(beginOffset, endOffset - beginOffset);
+        }
+    }
+}