I have Visual Studio Online (now VS Team Services) account as a part of my MSDN subscription. I managed to create a project there, set a workspace in my local Visual Studio 2013
I don't think you can currently, however it used Monaco editor, which is the same editor as sky drive uses for code files. So it may be that Microsoft are planning to add this in at some point.
Edit: Turns out they are planning on adding it, at lease for azure web sites, I found this article on tech cruch: http://techcrunch.com/2013/11/13/microsofts-visual-studio-2013-launches-with-new-online-tools-for-team-and-build-management-preview-of-browser-based-code-editor/