Labels should line break at hyphens

[1ec5]

Labels are often line-wrapped at spaces but never at hyphens, resulting in unwieldy or unbalanced labels. POIs like place names are often hyphenated, particularly in French-speaking countries but pretty much anywhere.

#1223 is similar, but hyphens are probably a more manageable problem at this stage.

/cc @ansis @mikemorris @nickidlugash

[peterqliu]

js equivalent mapbox/mapbox-gl-js#1115