Change the button creation code to use an array

— I feel like this is a slightly less inscrutable way of generating the button/hamburger markup
- Previously `settings.parentTag` was being closed with `</a>`
  - I'm assuming this was generally never raised as an issue because most people are probably using anchor links as parent tags anyway
  - Failing to do so would possibly be cleaned up by jQuery's html creation code, but better to be sure (and correct!)
Merge pull request #46 from roc/burgerArray

Change the button creation code to use an array*