Automatic sizing for text (#5)

[wilkox]

Add automatic text sizing using ggfittext, as suggested in #5. The example plots in the README now look like this:

[codecov-io]

Codecov Report

Merging #9 into master will increase coverage by 0.13%.
The diff coverage is 93.75%.

@@            Coverage Diff             @@
##           master       #9      +/-   ##
==========================================
+ Coverage   92.43%   92.57%   +0.13%     
==========================================
  Files          39       39              
  Lines        1111     1104       -7     
==========================================
- Hits         1027     1022       -5     
+ Misses         84       82       -2

Impacted Files	Coverage Δ
R/bar_plot.R	90.9% <ø> (ø)	⬆️
R/plot_types.R	33.33% <0%> (+1.33%)	⬆️
R/plot_num.R	96.42% <100%> (+0.08%)	⬆️
R/plot_imb.R	100% <100%> (ø)	⬆️
R/plot_cat.R	99.09% <100%> (-0.01%)	⬇️
R/add_annotation_to_bars.R	100% <100%> (ø)	⬆️
R/plot_mem.R	100% <100%> (ø)	⬆️

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[alastairrushworth]

Hi @wilkox thanks for this PR, I really like the ggfittext package, I think this is a great feature! I have now merged this into master. I might make a few follow-up edits to make sure the defaults make sense etc, but I think things look great.

I'll add a line in the NEWS.md file crediting the change to you. Let me know if there is any other way you'd expect to be credited (this is the first PR I've merged!).

[wilkox]

Thanks @alastairrushworth!