nitdoc: All methods are displayed in Classes description

Adding some functions which allow to get all methods defined and refined
and display them in the class page associated

Signed-off-by: Stefan Lage <lagestfan@gmail.com>
nitdoc: abstract some functions to Apropdef type

Abstract some functions to use inherited them for AMethPropdef and
ATypePropdef

Signed-off-by: Stefan Lage <lagestfan@gmail.com>
nitdoc: Added formal type in class description

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