Revising the bpugraph concept

We need a public but very limited ANode and BNode class
It can be used with ItemSetTraits and with some special maps

By example:
DescriptorMap<Graph, ANode>
InvertableMap<Graph, ANode, string>
IterableBoolMap<Graph, ANode>
IterableIntMap<Graph, ANode>
IterableValueMap<Graph, ANode, string>

Document: lemon-refman

Title: LEMON Reference Manual

Author: LEMON Development Team

Abstract: Documentation of LEMON.

Section: unknown

Format: HTML

Index: /usr/share/doc/lemon/html/index.html

Files: /usr/share/doc/lemon/html/*.html