Update 'Enums'

Enums.md

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+Enums "enumerate" a pre-existing type, most likely an Int.
+
+```
+enum ro Weekday:Int
+	sunday
+	monday
+	tuesday
+	wednesday
+	thursday
+	friday
+```
+
+Enum members can have explicitly defined values, but if they don't, their value
+is just incremented up from zero.
+
+Enum members are accessed similar to object members:
+
+```
+set day:Weekday Weekday.thursday
+```