#1 Define incompatible linktypes

[Sam Thiriot]

Currently, linktypes are "incompatible", meaning that once a link of type T1 was created between two agents A1 and A2, no other link can be created between A1 and A2.
This principle appears to be true in the previous applications; for instance, being the father of a girl means that you cannot marry her. This kind of social rule is rarely transgressed.
However, this simplification may limit the flexibility of the generator. Depending to the linktypes defined by the user, linktypes may be compatible. Ex: A1 and A2 may be neighbors, but also have a family relationship, or even watch any football match.
Suggestion, in short: allow the definition of sets of incompatible links, others being supposed to be compatible by default.