Fix Issues #136 and #138

[mstackhouse]

Types of changes

• [X] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [X] Breaking change (fix or feature that would cause existing functionality to change)
• [X] I have read the CONTRIBUTING document.
• [X] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [X] I have updated the documentation accordingly.
• [X] I have added tests to cover my changes.
• [X] All new and existing tests passed.

A couple of things packed in here:

• A fix has been made for #136 and I've verified the results against the original issue. The fix ended up being relatively complicated because of how the internals work. We actually didn't have unit tests that specifically cover that circumstance. denoms_by testing was done with other variables, but not specifically around the use of cols. Snapshot tests were added and the data in the data.frame output manually verified.
• While working on the unit tests, some messages popped up for deprecated functions (causing the unit tests to fail). Fixes for this were made. The deprecation of rlang::call_standardise() was quite significant. I basically did a static import of the function (and carried the license over) and this works because none of the rlang functions used within call_standardise() were internals, and none of the other functions were deprecated. Ideally I could have found a way around it, but the the use of the function was integral to modify_nested_call() and the functionality is not at all straightforward to recreate cleanly otherwise.
• I've also taken this as an opportunity to clean up snapshot tests that were done using a tibble. The print method of tibbles changes with the weather, making the snapshots extremely unreliable. Instead of making a significant change to those tests, I converted the tibbles to data.frames whose print methods are more consistent and the text of cells aren't truncated, so it makes the tests themselves more reliable. The changes were cross checked and I made sure that the existing tests was still technically passing before accepting the new snaps.

[mstackhouse]

@elimillera this is ready for review. The primary bug being fixed (#136) has been tested by the issue reporter.

[mstackhouse]

Update DESCRIPTION to note forcats needs to be 1.0.0 or greater because the fct_na_value_to_level isn't present in forcats 0.4.0 (https://forcats.tidyverse.org/news/index.html#forcats-100)

@elimillera updated. Is that the only issue?