case branches support constant sets for convenience

tests/accept/run/tcase_setconstr.nim

@@ -0,0 +1,15 @@
+discard """
+  output: "an identifier"
+"""
+
+const
+  SymChars: set[char] = {'a'..'z', 'A'..'Z', '\x80'..'\xFF'}
+
+proc classify(s: string) =
+  case s[0]
+  of SymChars, '_': echo "an identifier"
+  of {'0'..'9'}: echo "a number"
+  else: echo "other"
+
+classify("Hurra")
+