Add es package

Looking for some feedback on this approach to talking to ES.
There is no point in avoiding ReadAll when you're going to return the entire contents as a slice of strings anyway. Avoiding ReadAll is worth is when you can process data without using O(n) memory. Even more so as it looks like ES returns everything on a single line anyway.

(I still suggest using ReadAll in this case, but for future reference,
bufio.Scanner already has functionality for splitting on words:

	scanner := bufio.NewScanner(resp.Body)
	var indices []string
	scanner.Split(bufio.ScanWords)
	for scanner.Scan() {
		indices = append(indices, scanner.Text())
	}

)