settings.scope is never used

[viveleroi]

I grabbed this plugin as a quick and dirt solution for some documentation and it works well, except the scope wasn't being used. I'd submit a PR but it's a tiny change.

Line 43 should be changed from:

$.find(settings.header_tags.join (', ')).not(settings.exclude).each (function () {

to:

settings.scope.find(settings.header_tags.join (', ')).not(settings.exclude).each (function () {

The original was simply finding all headers in the document but the second only finds the matches in the provided scope.

Thanks!