Replaced experimental .contains()

The String.prototype.contains() method is only supported in Firefox, so I have
replaced it with .indexOf() which has better support.
Replaced .startsWith() with .indexOf

the startsWith() method is experimental and only supported by Firefox. Replaced
with indexOf() for better cross-browser compatibility.
Merge pull request #11 from SignalK/remove-call-to-contains

Maintenance change to docson, I think this can be merged without discussion