Add vendor files for go build

vendor/github.com/docopt/docopt-go/error.go

@@ -0,0 +1,49 @@
+package docopt
+
+import (
+	"fmt"
+)
+
+type errorType int
+
+const (
+	errorUser errorType = iota
+	errorLanguage
+)
+
+func (e errorType) String() string {
+	switch e {
+	case errorUser:
+		return "errorUser"
+	case errorLanguage:
+		return "errorLanguage"
+	}
+	return ""
+}
+
+// UserError records an error with program arguments.
+type UserError struct {
+	msg   string
+	Usage string
+}
+
+func (e UserError) Error() string {
+	return e.msg
+}
+func newUserError(msg string, f ...interface{}) error {
+	return &UserError{fmt.Sprintf(msg, f...), ""}
+}
+
+// LanguageError records an error with the doc string.
+type LanguageError struct {
+	msg string
+}
+
+func (e LanguageError) Error() string {
+	return e.msg
+}
+func newLanguageError(msg string, f ...interface{}) error {
+	return &LanguageError{fmt.Sprintf(msg, f...)}
+}
+
+var newError = fmt.Errorf