hplot: properly handle hstacks with bands and log-y

[sbinet]

Fixes #749.

[sbinet]

@rmadar this fixes your issue.
but uncovers a new one: notice the gray band over the empty bin, on the lower left tile plot (around -6)?

it would seem we may need to change how we draw H1D.Band.
instead of reusing hplot.Band, we may need to introduce a dedicated plotter (probably one that is just a bunch of polygons)

[codecov]

Codecov Report

Merging #750 into master will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #750      +/-   ##
==========================================
+ Coverage   71.55%   71.58%   +0.02%     
==========================================
  Files         384      384              
  Lines       49103    49111       +8     
==========================================
+ Hits        35135    35155      +20     
+ Misses      11709    11699      -10     
+ Partials     2259     2257       -2     

Impacted Files	Coverage Δ
hplot/h1d.go	93.37% <100.00%> (+0.12%)	⬆️
hplot/hstack.go	80.50% <100.00%> (+7.89%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 4cf183c...24781f7. Read the comment docs.

[rmadar]

OK I noticed the problem around -6, indeed. You mean that error band of histograms would need to be a different type than hplot.Band, at least for the plotting side?

Since we are about modifying error band of histograms, I had a suggestion in mind for a while (I might open a new issue if that's tricky): would it be possible to have hatched areas instead of full colored area? This looks way nicer for such a band:

[sbinet]

OK I noticed the problem around -6, indeed. You mean that error band of histograms would need to be a different type than hplot.Band, at least for the plotting side?

yep.
hplot.ErrBand ? with, at its core, a []plotter.Polygon.

Since we are about modifying error band of histograms, I had a suggestion in mind for a while (I might open a new issue if that's tricky): would it be possible to have hatched areas instead of full colored area? This looks way nicer for such a band:

that's gonum/plot#564