Arbitrary precedence graphs

[leonlan]

This issue discusses how to include arbitrary precedence graph data in the FJSPLIB format.

[leonlan]

I'm already feeling some friction with precedences right now in the classic FJSPLIB format:

• The precedence constraints are implicit. Namely, for each job, the precedence relationships are defined by the ordering of the operations.
• The first question is: do we include precedences in the parsed instance data? Or do we just simply return None?
• The second question is: do we write precedence data?
• Now answer the first question and second question in the context of arbitrary precedence graphs, i.e., a list of arcs.