Caption support (#2462)

Co-authored-by: WithoutPants <53250216+WithoutPants@users.noreply.github.com>

vendor/github.com/asticode/go-astikit/flag.go

@@ -0,0 +1,48 @@
+package astikit
+
+import (
+	"os"
+	"strings"
+)
+
+// FlagCmd retrieves the command from the input Args
+func FlagCmd() (o string) {
+	if len(os.Args) >= 2 && os.Args[1][0] != '-' {
+		o = os.Args[1]
+		os.Args = append([]string{os.Args[0]}, os.Args[2:]...)
+	}
+	return
+}
+
+// FlagStrings represents a flag that can be set several times and
+// stores unique string values
+type FlagStrings struct {
+	Map   map[string]bool
+	Slice *[]string
+}
+
+// NewFlagStrings creates a new FlagStrings
+func NewFlagStrings() FlagStrings {
+	return FlagStrings{
+		Map:   make(map[string]bool),
+		Slice: &[]string{},
+	}
+}
+
+// String implements the flag.Value interface
+func (f FlagStrings) String() string {
+	if f.Slice == nil {
+		return ""
+	}
+	return strings.Join(*f.Slice, ",")
+}
+
+// Set implements the flag.Value interface
+func (f FlagStrings) Set(i string) error {
+	if _, ok := f.Map[i]; ok {
+		return nil
+	}
+	f.Map[i] = true
+	*f.Slice = append(*f.Slice, i)
+	return nil
+}