Add exposed

[ChrisJones687]

Adding exposed file option to have both infected and exposed at the start of the simulation.

[codecov[bot]]

Codecov Report

Merging #92 (813cdac) into master (4600da2) will decrease coverage by 0.06%. The diff coverage is 78.57%.

:exclamation: Current head 813cdac differs from pull request most recent head f34e4c5. Consider uploading reports for the commit f34e4c5 to get more accurate results

@@            Coverage Diff             @@
##           master      #92      +/-   ##
==========================================
- Coverage   75.17%   75.11%   -0.07%     
==========================================
  Files          39       39              
  Lines        4589     4606      +17     
==========================================
+ Hits         3450     3460      +10     
- Misses       1139     1146       +7     

Impacted Files	Coverage Δ
R/auto_manage.R	0.00% <0.00%> (ø)
R/configuration.R	84.93% <77.27%> (-0.31%)	:arrow_down:
R/calibrate.R	90.80% <100.00%> (-0.50%)	:arrow_down:
R/pops.r	100.00% <100.00%> (ø)
R/pops_multirun.R	94.22% <100.00%> (+0.01%)	:arrow_up:
R/validate.R	99.37% <100.00%> (+<0.01%)	:arrow_up:

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[ChrisJones687]

closes #89