* Main gyp files are now standardized as platform/<platform>/platform.gyp.
* Each platform gyp file defines appropriate loop_lib and headless_lib variables.
* Each platform gyp file includes mbgl.gypi, which defines base targets which may be useful to all platforms.
* CI targets are consistent across platforms: `make $(PLATFORM) && make test-$(PLATFORM)`.
* Renamed the "linux" test app to "glfw". It's now built in OS X CI.
* Android build flakiness is fixed.
* iOS CI builds the bench and iosapp targets.
* Mesa version is now in one place.
* CI scripts use bash "strict mode" and correct error handling.
* All build output goes to the build directory.
* Removed vestigial iOS/OS X/Android Travis scripts.
The defaults remains the same: Bay area at zoom 15.
The key, if not supplied, is taken from the environment.
```
Allowed options:
-s [ --style ] URL Map stylesheet
--north degrees (=37.200000000000003) North latitude
--west degrees (=-122.8) West longitude
--south degrees (=38.100000000000001) South latitude
--east degrees (=-121.7) East longitude
--minZoom number (=0) Min zoom level
--maxZoom number (=15) Max zoom level
--pixelRatio number (=1) Pixel ratio
-t [ --token ] key Mapbox access token
-o [ --output ] file (=offline.db) Output database file name
```
