fixed highlighting

Signed-off-by: Guyzmo <guyzmo+github@m0g.net>
added timer function that polls regularly whether the text has been updated ;
added function parameter support for the Etherpad command ;
refactored update callback to update only the text object local to vim and mark it as updated (avoid thread safety problems) ;
added comments

Signed-off-by: Guyzmo <guyzmo+github@m0g.net>