Add .editorconfig to enforce existing style

.editorconfig

@@ -0,0 +1,14 @@
+# EditorConfig file: http://EditorConfig.org
+
+# top-most EditorConfig file
+root = true
+
+[*]
+end_of_line = lf
+insert_final_newline = true
+
+[*.d]
+charset = utf-8
+indent_style = space
+indent_size = 4
+trim_trailing_whitespace = true