Comments:
* I like the \\ for forcing a newline
* I think four hyphens, no more, no less, should translate to <hr/> (i
realise your proposal is not different from current syntax)
* I don't like that your image syntax is like <<image foo.png>>
instead of <<image:foo.png>>, this is inconsistant with the rest of
the syntax.
* I'd like «« an »» better than << and >>
* I like the syntax for **boldface text**, //italic text//,
$$typewriter text$$, ^^superscript^^, and __subscript__.