func (f FlagMap) copyMissingValues(m FlagMap, copyDefault bool) {
	for k, v := range m {
		if _, ok := f[k]; !ok {
			if !copyDefault && v.IsDefault {
				continue
			}
			f[k] = v
		}
	}
}
copyMissingValues adds all missing values to the flags map.
package grumble
import (
	"fmt"
	"time"
)
type FlagMapItem struct {
	Value     interface{}
	IsDefault bool
}
type FlagMap map[string]*FlagMapItem