Added Firepad insertHtml, insertText, insertTextAtCursor

What do you think of this? 

There's just one thing that needs fixing but I wanted your feedback before touching it. 

      function insertLine(line) {
        if (!atNewLine)
          insert('\n');

How is atNewLine used? It currently results in a new blank line being inserted before any insert. Seems to be that removing the atNewLine thing works fine... But there must be a reason it's here ;-)