Add support for population size changes in aevol_modify

I suppose there was some kind of mistake with the last commit (Fix memory leak due to indiv not deleted) since the only thing it does is it removes an empty line...

Could you please double check?

added 183 commits

• 081657d9...48cb2ae8 - 178 commits from branch aevol:aevol-9
• a9fa8dee - First implementation of population size modification
• 43c0f0de - Exports corresponding ids into csv file and logs population modifications
• cc267c01 - Fix last segfault caused by destructors
• d14ba75a - Require global selection scope
• 29b58bb0 - Fix memory leak due to indiv not deleted

Compare with previous version

FYI I'be rebased onto the latest aevol-9 and fixed some indent issues

added 37 commits

• 29b58bb0...19a06d2a - 30 commits from branch aevol:aevol-9
• 03598083 - WIP: output txt version of the tree
• e273fea8 - WIP output txt version of the lineage
• 1b61e45b - First implementation of population size modification
• ac9b9f22 - Exports corresponding ids into csv file and logs population modifications
• 552f234e - Fix last segfault caused by destructors
• 0136b239 - Require global selection scope
• f6eea9e9 - Fix memory leak due to indiv not deleted

Compare with previous version

added 5 commits

• 6b117678 - First implementation of population size modification
• 3d4e3dd4 - Exports corresponding ids into csv file and logs population modifications
• e28a506d - Fix last segfault caused by destructors
• 17e52b1c - Require global selection scope
• 6cc7ed9a - Fix memory leak due to indiv not deleted

Compare with previous version

mentioned in commit 690fc847

merged