parse min-zoom/max-zoom values

refs mapbox/mapbox-gl-style-spec#65
skip bucket creation if it's out of range
refactor source information into SourceInfo object
pass SourceInfo object to TileData so that we can not skip buckets that appear later than the source maxzoom
support fractional min/max-zoom values
skip rendering layer when min/max-zoom condition isn't met
respect layer min/maxzoom, not source min/maxzoom
Show where to edit scheme
Flip name and units and sign of rotation API

Angle -> Bearing
Radians -> Degrees
Clockwise -> Counterclockwise
Use mapbox-gl-test-suite
Fix sprite->pos data race
do not explicitly render matte; we already cleared the background with glClear
read default values from property structs

fixes background color
include what you use
more include what you use
bump cocoa bindings

fixes #374
fix text placement

[skip ci]
reduce maxPlacementScale

implements https://github.com/mapbox/mapbox-gl-js/commit/871883d569c932137d00b045eb47e14f4798ebc5
bump Cocoa for bearing sign/units fixes
refs #318 & #378: OS X install doc tweaks