Add a div with cython class for embedding

This allow to reuse directly the body and embed it without having to
wrap it in the correct div and have the CSS apply to it.

--HG--
extra : amend_source : 9e1c6980d3fd2fa2d1cd0e882f7e186c3a08c7e5

Clean html-annotate generation

special_char was use before for counting column offset, now removed.
replace by escape_html

generated html can be added many time in one page relying on line number
to collapse is dangerous.

Walking the dom to  get next children is more reliable

add a directive to disable SwitchTransform

Previously cython.inline didn't correctly handle variables
declared in nested scopes (such as function declarations).

in particular tings like 'code' are conflicting when embeding the page

will allow refactor of the cython magic not to parse temporary files
and not to leak css into IPython notebooks

SwitchTransform is unable to detect all cases of duplicate values, which
result in errors at compile time in the generated code.

this should help to decouple from the filesystem and heuristic in
filenames