$.fn.markdown.defaults.iconlibrary = 'fa';
$.fn.markdown.defaults.buttons[0][0]['data'][2]['icon']['fa'] = 'fa fa-heading';
$.fn.markdown.defaults.buttons[0][1]['data'][1]['icon']['fa'] = 'fa fa-image';
$.fn.markdown.defaults.buttons[0][2]['data'][1]['icon']['fa'] = 'fa fa-list-ol';