Go version is not Unicode safe

[tsak]

Hi Kyle,

Came across your blog post when searching for "golang xor encryption" and was testing it. Unfortunately, your function isn't Unicode safe. I've created a few test cases in https://play.golang.org/p/UdCubbEZECx to show the issue.

Might be worth putting a warning into the code/blog post, as string handling in Go has its gotchas unfortunately.

Thanks, tsak