Calling fmt.Printf("%v") on a DynamoDBAttributeValue causes mini-panic

[keyneston]

When you call fmt.Printf("%v") on any non-String events.DynamoDBAttributeValue a panic gets embedded into your string.

Example:

package main

import (
	"fmt"

	"github.com/aws/aws-lambda-go/events"
)

func main() {
	v := events.NewNumberAttribute("5")
	fmt.Println("This is a number: %v", v)
}

Outputs:

$ go run bugreport.go
This is a number: %v %!v(PANIC=String method: accessor called for incompatible type, requested type 8 but actual type was 5)

As far as I can tell this is due to the fact that you are using .String() as the function to get back a string from the attribute. This conflicts with the fact that .String() is also the interface used for printing.

aws-lambda-go/events/attributevalue.go

Line 94 in ec2fec7

av.ensureType(DataTypeNumberSet)

[bmoffatt]

Merged #226