Zombie species

[evadelmas]

Fixes #77

This PR changes the Callback conditions in the simulate function to better detect extinctions. It also introduces the possibility to control the extinction threshold and the number of interpolated points through the following keywords:

• extinction_threshold (default to 1e-6)
• cb_interp_points (default to 100)

[codecov]

Codecov Report

Merging #78 into next will increase coverage by 0.2%.
The diff coverage is 88%.

@@           Coverage Diff            @@
##            next      #78     +/-   ##
========================================
+ Coverage   84.7%   84.91%   +0.2%     
========================================
  Files         16       16             
  Lines       1020     1034     +14     
========================================
+ Hits         864      878     +14     
  Misses       156      156

Impacted Files	Coverage Δ
src/simulate.jl	89.58% <88%> (+4.28%)	⬆️

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[coveralls]

Coverage increased (+0.2%) to 89.206% when pulling 066db56 on zombie_species into f2d74cd on next.