Use the specific config structure for each command

[alonlong]

Now there are different flagsets for different commands, but for each command, it uses a global config structure:

type Config struct {
    Version bool
    Agent     Agent     `skip:“true”`
    Server    Server    `skip:“true”`
    Convert   Convert   `skip:“true”`
    Exec      Exec      `skip:“true”`
    DbManager DbManager `skip:“true”`
}

just like the server command, the function is like this:

func startServer(cfg *config.Config)

i think it's better to use its own config for each command, the function should be like this:

func startServer(cfg *config.Server)