Add editorconfig file to try to enforce code style

This makes it easier for those with different Visual Studio (or
other editor) settings to contribute since it will help ensure
whitespace (and other style choices) remains uniform.

.editorconfig

@@ -0,0 +1,10 @@
+# EditorConfig: http://EditorConfig.org
+root = true
+
+[*]
+end_of_line = crlf
+insert_final_newline = true
+charset = utf-8
+
+[*.cs]
+indent_style = tab