Make userdata fields/properties/methods case insensitive

While this can potentially cause collisions, this allows us to easily use Lua's style guide

UpsilonTests/UserDataTests.cs

@@ -47,7 +47,7 @@ namespace UpsilonTests
             var obj = new UserDataHelper();
             const string input = @"
 function test(o)
-    return o[""FieldString""]
+    return o.fieldString
 end
 ";
             var script = new Script(input);
@@ -63,7 +63,7 @@ end
             var obj = new UserDataHelper();
             const string input = @"
 function test(o)
-    o[""FieldStringSet""] = ""Test""
+    o.FieldStringSet = ""Test""
 end
 ";
             var script = new Script(input);
@@ -79,7 +79,7 @@ end
             var obj = new UserDataHelper();
             const string input = @"
 function test(o)
-    o[""TestMethod""]()
+    o.testMethod()
 end
 ";
             var script = new Script(input);
@@ -95,7 +95,7 @@ end
             var obj = new UserDataHelper();
             const string input = @"
 function test(o)
-    return o[""Add""](100, 20)
+    return o.add(100, 20)
 end
 ";
             var script = new Script(input);