Alias Escape to html.EscapeString

[`html.EscapeString`][1] is [more complete][2] and thus should be used instead.

This also closes #9, but it is based on top of #17, so merging this will also merge #17.

[1]: http://golang.org/pkg/html/#EscapeString
[2]: http://golang.org/src/pkg/html/escape.go?s=5317:5351#L219