reduce glyph downloads

[ansis]

Without panning, debug/#14.56/35.684347/139.748227/0.0 loads 13MB of font stuff

[mikemorris]

Ouch. This is the problem of CJK glyphs being scattered all over the massive ranges, so even breaking this into 256-glyph chunks isn't helping.

[yhahn]

I think next steps here would be doing an analysis of glyph usage in these ranges using a large body of CJK text like all OSM labels that fall in this range. Commonly used glyphs may not fall into the same ranges but maybe we will learn there is a subset of glyphs that could be bundled together and handle a majority of uses.

[mikemorris]

Agreed @yhahn, think we can be smarter about optimal glyph ranges with a little analysis.

[yhahn]

Let's track here: mapbox/node-fontnik#36