Add {units} compatibility with majority-vote for best units

[cregouby]

This is an opinionated PR to make pretty_num work with class("units") number. I'm not confortable with the package dependencies impact. I think it would be much cleaner to turn both impacted functions into S3 methods and split the "units::" part of this P.R. into a P.R. to the {units} team

[codecov-io]

Codecov Report

Merging #28 (0349006) into master (b1cdad8) will increase coverage by 5.24%. The diff coverage is 79.03%.

@@            Coverage Diff             @@
##           master      #28      +/-   ##
==========================================
+ Coverage   65.26%   70.51%   +5.24%     
==========================================
  Files           4        5       +1     
  Lines          95      156      +61     
==========================================
+ Hits           62      110      +48     
- Misses         33       46      +13     

Impacted Files	Coverage Δ
R/numbers.R	78.33% <78.33%> (ø)
R/sizes.R	18.42% <100.00%> (+2.20%)	:arrow_up:

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[gaborcsardi]

Thanks! I updated this, so it could be merged. However, it would be great to drop the hard dependency on units.

Maybe we can move it to Suggests?

Also, the current implementation fails, because it seems that we cannot compare 'units' objects and regular numbers any more:

library(units)
l_cm <- set_units(1337129, cm)
pretty_num(l_cm)
#> Error in Ops.units(amt, as.integer(amt)) :
#>   both operands of the expression should be "units" objects

l_cm < 0
#> Error in Ops.units(l_cm, 0) :
#>   both operands of the expression should be "units" objects

[cregouby]

I'll have a look this week on it...