Change to using typed docstrings.

An URL, filename (or other identifier) might also be a possible option. If someone wants to create a IDE where you can have rich WYSIWYG editor with images/graphs/audio in a method documentation, it would be nice to have it accessible from Julia `help()` as well. An external identifier will drastically reduce the size of the source file. A base64 encoded image flows very badly if you have line wrapping in your text editor.