font.go
func NewFolderFontCache(folder string) *FolderFontCache {
	return &FolderFontCache{
		fonts:  make(map[string]*truetype.Font),
		folder: folder,
		namer:  FontFileName,
	}
}
func NewFolderFontCache(folder string) *FolderFontCache {
	return &FolderFontCache{
		fonts:  make(map[string]*truetype.Font),
		folder: folder,
		namer:  FontFileName,
	}
}
// NewFolderFontCache creates FolderFontCache