Printing code refactoring

[Enchufa2]

• Improved interface for activities (i.e., new internal::print + ARG macro).
• Improved interface for entities (Simulator::print).

[codecov]

Codecov Report

Merging #149 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master   #149   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          52     52           
  Lines        2852   2824   -28     
=====================================
- Hits         2852   2824   -28

Impacted Files	Coverage Δ
inst/include/simmer/activity/fork.h	100% <100%> (ø)	⬆️
inst/include/simmer/process/task.h	100% <100%> (ø)	⬆️
inst/include/simmer/resource/preemptive.h	100% <100%> (ø)	⬆️
inst/include/simmer/activity/arrival.h	100% <100%> (ø)	⬆️
inst/include/simmer/resource/priority.h	100% <100%> (ø)	⬆️
inst/include/simmer/activity/timeout.h	100% <100%> (ø)	⬆️
inst/include/simmer/activity/source.h	100% <100%> (ø)	⬆️
inst/include/simmer/process/manager.h	100% <100%> (ø)	⬆️
inst/include/simmer/activity/renege.h	100% <100%> (ø)	⬆️
inst/include/simmer/simulator.h	100% <100%> (ø)	⬆️
... and 11 more

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