Use log1p(x) instead of log(1+x)

[mllg]

log1p is numerically accurate for small x with 1 + x == 1:

x = 1e-20
log(1 + x)
log1p(x)

[codecov-io]

Codecov Report

Merging #39 into master will decrease coverage by 0.06%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #39      +/-   ##
==========================================
- Coverage      98%   97.93%   -0.07%     
==========================================
  Files           5        5              
  Lines         100       97       -3     
==========================================
- Hits           98       95       -3     
  Misses          2        2

Impacted Files	Coverage Δ
R/regression.R	100% <100%> (ø)	⬆️
R/information_retrieval.R	96.77% <0%> (-0.29%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update ca12765...d729087. Read the comment docs.

[mfrasco]

Thank you so much for the contribution to the package!