Rename existing interpolate -> resample
Consolidate duplicate interpolation definitions

While here, do not interpolate style properties that
are not transitionable. The previous behavior was to
switch from old to new value halfway through the transition;
now the new value is used immediately, as in JS.
compute unique clip ids per tile, taking covering children into account

fixes #206
fixes #220
refs #229
add missing file
don't duplicate function
don't trip up certain stdlib implementations
add != operator for certain stdlib implementations
add a few fixes for gcc

fixes #437
remove unused threadpool class
never place infinitely deep symbols
also use boost codecvt on linux
use correct implementation
Load TileJSON; support inline TileJSON sources

Fixes #412
Refs https://github.com/mapbox/mapbox-gl-style-spec/pull/143
use platform-specific NSString for case changes on OS X/iOS

refs #309
add uppercase/lowercase symbols to headless test
use submodule version for ios build
increase build concurrency
Use float for pixelRatio
Indicate gzip support as well as deflate

libcurl supports both: http://curl.haxx.se/dev/readme-encoding.html
Fix headless tests