Heterogeneity interruption

[dushoff]

There should be a way to interrupt a too-slow or frozen simulation. If there already is such a way it should be documented more prominently.

[pearsonca]

this is sort of addressed in useclinc branch by doing simulation in bite sized blocks (50 per GO! after part 1) and putting a relatively small upperbound on the number of simulations to add in part 1 (50).