Update & Create Sass version of CSS

• Move demo css into it's own file

• Update menu icon to be built from 1 span tag using :before & :after selectors to build the other two bars.  -- update demo.html, query.meanmenu.js & readme.md to reflect this change

• Replace <'s with &lt;'s on line 55 of readme, as they weren't rendering

• Add new scss file and compiled CSS and minified CSS files