Fixed behavior of within to remove special case.

>The value 2 should return -1. 2 is <= s[0], but it is not < s[1]. I don't think anything can be done.

Oh god, I'm sorry. I think it should return 0 actually - though this goes against the terms of the docs as they stand.

Why not:

	for i, f := range s[:len(s)-1] {
		switch {
		case v >= f && v < s[i+1], v == f && f == s[i+1]:
			return i
		}
	}


Shoot me.

>s := []float64{1,1,1,1}

>What should Within(s, 1) return? It seems to me the only reasonable answer is -1.

Someone who has created that gets what they deserve.