Bugfix and documentation formatting for simcam performance stats

[svonallmen]

• Fixed a typo which lead to a bug in simcam.getPerformanceStats, returning implausible and asymmetrical results.
• Made the documentation for plotModelDistance.simcam more readable by using an enumerated list, and fixed a typo.

[codecov-commenter]

Codecov Report

Merging #91 into master will increase coverage by 0.00%. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master      #91   +/-   ##
=======================================
  Coverage   87.91%   87.91%           
=======================================
  Files          29       29           
  Lines        4659     4644   -15     
=======================================
- Hits         4096     4083   -13     
+ Misses        563      561    -2     

Impacted Files	Coverage Δ
R/simcam.R	94.26% <100.00%> (ø)
R/mcrpure.R	85.29% <0.00%> (-0.14%)	:arrow_down:

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[svkucheryavski]

Thanks a lot!