Merge pull request #134 from mattes/expose-isset-via-getter

expose isSet via getter
diff --git a/option.go b/option.go
index 29e702c..d337a62 100644
--- a/option.go
+++ b/option.go
@@ -155,3 +155,8 @@
 func (option *Option) Value() interface{} {
 	return option.value.Interface()
 }
+
+// IsSet returns true if option has been set
+func (option *Option) IsSet() bool {
+	return option.isSet
+}