C++ code refactoring (closes #145)

[Enchufa2]

No description provided.

[codecov]

Codecov Report

Merging #147 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master   #147   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          22     52   +30     
  Lines        2891   2848   -43     
=====================================
- Hits         2891   2848   -43

Impacted Files	Coverage Δ
src/activity.cpp	100% <ø> (ø)
inst/include/simmer/process/order.h	100% <100%> (ø)
inst/include/simmer/entity.h	100% <100%> (ø)
inst/include/simmer/simulator.h	100% <100%> (ø)
inst/include/simmer/process/task.h	100% <100%> (ø)
inst/include/simmer/process/arrival.h	100% <100%> (ø)
inst/include/simmer/activity/leave.h	100% <100%> (ø)
inst/include/simmer/activity/utils/functions.h	100% <100%> (ø)
inst/include/simmer/monitor.h	100% <100%> (ø)
inst/include/simmer/activity/rollback.h	100% <100%> (ø)
... and 75 more

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