Allow integers as input

[MethodGrab]

At the moment if you pass an integer to the polyfill it will error because doing charAt() on an integer isn't valid.

I know the docs for the native version of btoa state that the input should be a string but both Chrome & Firefox allow integers to be used without erroring so I think not erroring on integers would be in-line with how someone would expect the polyfill to work.

[davidchambers]

This sounds reasonable to me. It should be as simple as applying String to the argument:

> btoa(42) === btoa('42')
true
> btoa(null) === btoa('null')
true
> btoa({x: 1}) === btoa('[object Object]')
true

[MethodGrab]

Great, thanks David!

[davidchambers]

No problem. Thanks for the suggestion.