Compute and print time elapsed

[patr1ckm]

This computes and prints the elapsed time when fitting the model for both fit_xy and fit.

Fixes #175 .

[codecov-io]

Codecov Report

Merging #224 into master will increase coverage by 0.17%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #224      +/-   ##
==========================================
+ Coverage   75.81%   75.98%   +0.17%     
==========================================
  Files          38       38              
  Lines        2931     2936       +5     
==========================================
+ Hits         2222     2231       +9     
+ Misses        709      705       -4

Impacted Files	Coverage Δ
R/fit.R	81.81% <100%> (+2.73%)	⬆️
R/fit_helpers.R	96.55% <100%> (+0.12%)	⬆️

---

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 3fef9c3...582def3. Read the comment docs.

[topepo]

Can you use system.time() instead? Also, use the prettyunits package to print the total elapsed time.

[patr1ckm]

prettyunits is great, thanks! Here's how it looks:

[topepo]

Excellent. Thanks

[github-actions]

This pull request has been automatically locked. If you believe you have found a related problem, please file a new issue (with a reprex: https://reprex.tidyverse.org) and link to this issue.