Reconnect DB after closing.

[ofofofofo]

Description

If this is a feature request, explain why it should be added. Specific use-cases are best.

For bug reports, please provide as much relevant info as possible.

When Connection closed, it unable to open again.

Steps to Reproduce the Problem

Please describe in painful detail what you did (so others can play along with you) to get to this point. This includes things like the exact command(s) you used, or the curl command you used, that sort of thing.

	users := []User{}
	for i := 0; i < 2; i++ {
		conn, err := pop.Connect("development")
		if err != nil {
			fmt.Println(err)
		}
		err = conn.All(&users)
		if err != nil {
			fmt.Println(err)
			os.Exit(1)
		}
		for _, u := range users {
			fmt.Println(u)
		}
		err = conn.Close()
		// conn.Store = nil // make Store to nil will continue the loop
		if err != nil {
			fmt.Println(err)
		}
	}

Expected Behavior

connection will recconnect after closing

Actual Behavior

unable to fetch records: sql: database is closed

Info

Should set Store = nil in Connection's Close method.

[sio4]

Indeed, it could be an issue in a complex application that need to control the connection state. will fix.