allow changing size of ridgelines

[jgabry]

Based on this issue reported on the forums

https://discourse.mc-stan.org/t/bayesplot-mcmc-areas-line-and-grid-width-manipulation/16001

I added a size argument to mcmc_areas() and mcmc_areas_ridges() to control the size (thickness) of the ridgelines.

[jgabry]

Travis still isn't working because it times out, but tests pass locally for me.

[codecov-commenter]

Codecov Report

Merging #224 into master will decrease coverage by 0.09%.
The diff coverage is 33.33%.

@@            Coverage Diff             @@
##           master     #224      +/-   ##
==========================================
- Coverage   98.58%   98.49%   -0.10%     
==========================================
  Files          31       31              
  Lines        3969     3975       +6     
==========================================
+ Hits         3913     3915       +2     
- Misses         56       60       +4     

Impacted Files	Coverage Δ
R/mcmc-intervals.R	98.21% <33.33%> (-1.01%)	⬇️

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[jgabry]

All checks now passing via GitHub actions

[codecov-io]

Codecov Report

Merging #224 (fc63a9b) into master (665c687) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #224   +/-   ##
=======================================
  Coverage   98.35%   98.36%           
=======================================
  Files          32       32           
  Lines        4146     4156   +10     
=======================================
+ Hits         4078     4088   +10     
  Misses         68       68           

Impacted Files	Coverage Δ
R/mcmc-intervals.R	99.24% <100.00%> (+0.01%)	⬆️

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[jgabry]

Added visual tests and made sure axis expansion is sufficient to avoid cutting off top of the highest ridgeline (I checked plots with few parameters, medium number of parameters, and many parameters).

[tjmahr]

Just a couple of questions. Otherwise looks good to me.

[codecov-commenter]

Codecov Report

Merging #224 (e908354) into master (5555083) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #224   +/-   ##
=======================================
  Coverage   98.37%   98.37%           
=======================================
  Files          32       32           
  Lines        4187     4197   +10     
=======================================
+ Hits         4119     4129   +10     
  Misses         68       68           

Impacted Files	Coverage Δ
R/mcmc-intervals.R	99.24% <100.00%> (+0.01%)	⬆️

---

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Δ = absolute <relative> (impact), ø = not affected, ? = missing data
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