Added support for enums backed by types.

Author: InsertCreativityHere

syntaxes/slice.tmLanguage.json

@@ -700,6 +700,14 @@
               },
               "patterns": [
                 {"include": "#standard"},
+                {
+                  "begin": "(:)\\s*(\\w*)",
+                  "end": "(?=({|;))",
+                  "beginCaptures": {
+                    "1": {"name": "punctuation.storage.modifier.extends.slice"},
+                    "2": {"patterns": [{"include": "#storage.types"}]}
+                  }
+                },
                 {
                   "begin": "{",
                   "end": "(?=})",