Backport from SNN

[alessandropellegrini]

Backport:

• Retractable
• Pubsub

[alessandropellegrini]

Depends on #21.
Assign TAGS in MODELINIT, which are dynamically assigned by the runtime.

[alessandropellegrini]

@Piccions although still far from what we discussed, we should consider retractable as addressed by 282ad66 couldn't we?

[Piccions]

@Piccions although still far from what we discussed, we should consider retractable as addressed by 282ad66 couldn't we?

For the purposes of SNNs and simple ABM models, that retractable module is enough. I'll write some tests and clean the code a bit. I'll open a merge request in the next days.

[alessandropellegrini]

Good! I'm marking retractable as done. The new ScheduleNewEvent interface will deserve a new issue.

[alessandropellegrini]

@AdrianoPi I think the backport of the pubsub module will still take some time, won't it? Shall we move this to v3.1.0?

[AdrianoPi]

It likely will. We can move it to v3.1.0 which might make things smoother.