ni_nitdoc: Added overview body

Signed-off-by: Stefan Lage <lagestfan@gmail.com>
ni_nitdoc: Adding some functions in AModule class

Adding a function to get the comment of Amodule object and another to
get the short comment of it

Signed-off-by: Stefan Lage <lagestfan@gmail.com>
ni_nitdoc: Display all modules in Overview

Adding a function to insert in overview page all modules concerns in the
program

Signed-off-by: Stefan Lage <lagestfan@gmail.com>