Follows Moore!1996, changes in Functor's reference page

To be tested with Moore!1996 (merged)

Update the ThOr functors descriptions for the documentation. It helps to address (part of) #435.

• Create doctests for binary functors to improve documentation.
• Fix reference to other functors
• Fix link to TWiki pages
• Add inputs type for each functor
• Give a more meaningful description to some functors