[doc] fix path in makefile

provide a new RichString attribute type The follwing declaration: class Card(EntityType): content = RichString(fulltextindexed=True, default_format='text/rest') is equivalent to : class Card(EntityType): content_format = String(meta=True, internationalizable=True, default='text/rest', constraints=[format_constraint]) content = String(fulltextindexed=True)

chainfirst / chainall can be given a name argument to use as inner function's name