This change adds a <Operation>Pages() operation to each operation
with pagination configuration to return an iterator that can be
used like slice iteration:

	db := dynamodb.New(nil)
	for resp := range db.ListTablesPages() {
		fmt.Println(resp)
	}

References #58

New API:

	func main() {
		db := dynamodb.New(nil)
		params := &dynamodb.ListTablesInput{Limit: aws.Long(2)}
		i := 0
		db.ListTablesPages(params, func(p *dynamodb.ListTablesOutput, err error) bool {
			if err != nil {
				fmt.Println("An error occurred", err)
			} else if p != nil {
				i++
				fmt.Println(i, awsutil.StringValue(p))
			} else {
				fmt.Println("Finished paging!")
			}
			return true // return false to stop paging
		})

	}

Also adds pagination tests.

References #58

New API:

	numPages := 0
	err := req.EachPage(func(p *dynamodb.ListTablesOutput, last bool) {
		// Print a page of data
		numPages++
		fmt.Printf("Page %d: %x\n", numPages, p.TableNames)

		if last { // We are on the last page
			fmt.Println("Got to last page")
		}
	})

	if err != nil {
		panic(err)
	}

- Document use of nil reflect.Value with Call()
- Rename "result" to "shouldContinue"
- Use "SetValueAtAnyPath" to match case insensitive matches
- Copy parameters when sending new request (add test assertion for this)

Also refactor and add tests for truncation logic