add functions/vendor files

vendor/github.com/Azure/go-ansiterm/winterm/utilities.go

@@ -0,0 +1,9 @@
+// +build windows
+
+package winterm
+
+// AddInRange increments a value by the passed quantity while ensuring the values
+// always remain within the supplied min / max range.
+func addInRange(n int16, increment int16, min int16, max int16) int16 {
+	return ensureInRange(n+increment, min, max)
+}