Handle single & double quote

Should fix issue #27

This issue comes when in handlebars you have this kind of thing

```handlebars
{{{sprintf (gettext '<span class="counter">%s</span> foo' '<span class="counter">%s</span> foos' much) much }}}
```

It's a weird case where HTML is included in string to translate because you want another typo or font size for the variable but in a big long sentence. As you want to preserve localization, because in some other language the variable can be set in another place in the sentence, you include it in the sentence to translate.

So... double quote in the sentence...

And the hbs extractors transforms it to JS like function before calling execution in gettext context

```javascript
gettext("<span class="counter">%s</span> foo", "<span class="counter">%s</span> foos", 0)
```

See how double quote ruins everything.

This PR fixes it by choosing which quote to use, single or double.
To sum it up: before this PR

```
{{gettext.ngettext 'foo' 'foos'  much }}
```

produced

```
gettext.ngettext("foo", "foos", "undefined")
```

now it produce

```
gettext.ngettext("foo", "foos", 0)
```

Which is syntaxically more correct, but again, the third param has totally no influence in .pot generation.

And yeah it's a side effet of fixing the issue #27