Knitr imports fix

[mjskay]

The PR closes #60, and closes #61

Changes include:

• Adding some missing imports from knitr to Imports
• Reversing order of Imports and Suggests in DESCRIPTION
• Using a silly hack to suppress warnings against using :::. Basically I add `%:::%` = `...` to the top of any function that uses ::: (because we can't guarantee the %:::% thing is visible in some cases, also as a reminder to fix those functions later). Then you can replace any instance of package:::function(x,y) with ('package'%:::%'function')(x,y) inside that function and you won't get the warning :).

[mjskay]

The macOS-latest (devel) run is failing on github actions at the dependency install stage it seems (not on CHECK). My inclincation would be to turn it off. That's what I did with tidybayes / ggdist --- I've been running a windows instance for checking the devel version of R since it seems to be more reliable. I will switch over to that here too and see if that works.