Add input checking

[jamesmbaazam]

This PR will close #84, close #104, and fix #61.

[codecov-commenter]

Codecov Report

Merging #108 (a07b9f6) into main (fd81398) will increase coverage by 0.04%.
The diff coverage is 100.00%.

❗ Current head a07b9f6 differs from pull request most recent head 8693215. Consider uploading reports for the commit 8693215 to get more accurate results

@@            Coverage Diff             @@
##             main     #108      +/-   ##
==========================================
+ Coverage   98.58%   98.63%   +0.04%     
==========================================
  Files           8        8              
  Lines         425      511      +86     
==========================================
+ Hits          419      504      +85     
- Misses          6        7       +1     

Files	Coverage Δ
R/borel.r	94.44% <100.00%> (-5.56%)	⬇️
R/checks.R	100.00% <100.00%> (ø)
R/likelihood.R	98.55% <100.00%> (+0.21%)	⬆️
R/simulate.r	98.97% <100.00%> (+0.13%)	⬆️
R/stat_likelihoods.R	100.00% <100.00%> (ø)
R/utils.r	100.00% <100.00%> (ø)

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