Implement multi-node notation.

[dietercastel]

The string below should result in a network where each C node has a directed connection to F.
str1 = "C1,C2,C3>F"
Same for the undirected case of course:
str2 = "F-C1,C2,C3"

Both sides could be useful as well:
str3 = "A,B-C,D" This could expand to this: str3 = "D-A-C; D-B-C"

The advantages of 'expanding' the syntactic sugar like that is that the parser only needs an extra preprocessing step (right behind the cleaning up of spaces). But if you see another better solution feel free to pick that one.

First writing some tests cases for this (e.g. the above) would be a good start.

[dietercastel]

This is by no means a priority but a nice addition. :-)