Add support for SBML L3 Events

[jmrohwer]

During the 2nd semester of 2022 I supervised a bioinformatics Honours student (Hanri van Heerden) who worked on support for SBML L3 events in PySCeS. The following was implemented:

• handling of simultaneous events (i.e. triggered by the same trigger)
• implementation and handling of priorities as event attributes, which determine the order in which the events are to be executed (according to the SBML spec)

Implementation of the following attributes is still outstanding:

• InitialValue (currently hard coded to True)
• Persistent (currently hard coded to True)

SBML import and export (round tripping) works.

To implement this, the PSC input file syntax for events was expanded as follows:

Event: name, trigger, delay, priority {
    event assignments
    }

The newly introduced priority attribute (integer or None) is optional to deal with legacy PSC files. If it is not specified, the event priority attribute is assigned to None in the model.

Example notebook and model files demonstrating the implementation are available here. That repo also contains a copy of Hanri's Honours report for reference.

[bgoli]

Hi nice stuff, more by email.

[jmrohwer]

The events branch has been merged into development, so all further development can take place there as discussed.