Add annotations to nodes

[ftomassetti]

Think of case of processing goto and tags. We may want to mark them when they correspond to specific patterns.

[ftomassetti]

They may be also useful for associating the type. In general they would replace all external maps using the nodes as keys. They in a way permit to associate some piece of data defined externally to the Node and have that piece of data move around attached to the node.
They can be useful for all external applications elaborating the nodes.