new tester; all tests categorized

tests/astoverload/tastoverload1.nim

@@ -0,0 +1,21 @@
+discard """
+  output: '''string literal
+no string literal
+no string literal'''
+"""
+
+proc optLit(a: string{lit}) =
+  echo "string literal"
+
+proc optLit(a: string) =
+  echo "no string literal"
+
+const
+  constant = "abc"
+
+var
+  variable = "xyz"
+
+optLit("literal")
+optLit(constant)
+optLit(variable)