Improve package quality

[trinker]

The following tasks need to be done for improving the package quality:

• Add vignette
• Add unit test for >= 85% of code
• Fix all warnings in devtools::document related to missing links
• Remove deprecated functions

vignette

1. symlinking may be the solution: https://github.com/clarkfitzg/autoparallel/blob/master/README.md
2. Specialized function to copy all/portions of readme? (see: Proposed feature: README_to_vignette() r-lib/usethis#329)

tests

• Open call to anyone who wants an intro to PR in github and knows how to write unit tests