automatic height

[Fil]

closes #323

It's not dramatically affecting any of the test plots (for example test/plots/athletes-sport-sex.js' height was fixed manually at 500px, and becomes 508px with this heuristic).

[Fil]

I've revised all the test/plots/ :

• mobyDickFaceted, penguinMassSex and penguinMassSexSpecies have become ultra-high (e.g. 770px vs 400)
• morleyBoxPlot, movieProfitByGenre and ordinalBar have become short (160px, 320px and 200px) but I think it's ok
• caltrain and ballotStatusRace are just a bit too tall (I think we should give them a manual height)

(I think that athletes-sport-weight is also a bit too tall—540 would be nicer than 640—, but that's already a manual setting.)

[Fil]

the large height comes from
42d95b4#diff-30ab29a77cf3887e9e7e3ec68157a17e77e891ca7d6335074ab995ab1f27b82fR141

my solution is to consider that as soon as a chart has vertical facets, the auto height of a facet should be halved:

-  const nfy = fy ? fy.scale.domain().length : 1;
-  return !!(y || fy) * Math.max(1, Math.min(60, ny * nfy)) * 20 + !!fx * 30 + 60;
+  const nfy = fy ? fy.scale.domain().length : 2;
+  return !!(y || fy) * Math.max(1, Math.min(60, ny * nfy)) * 10 + !!fx * 30 + 60;

In the test plots this change impacts only: ballotStatusRace, mobyDickFaceted, penguinMassSex and penguinMassSexSpecies.

[mbostock]

I’ve committed a further tweak. I prefer that adding faceting does not affect the natural height of bands, but that if the subplots don’t have an ordinal y scale, that we partition the target height of 400px for each facet, but down to a minimum of ~140px for each facet.

[Fil]

(post-facto approved)