add cli tool for rendering a map to an image
show default values and allow setting the output filename
add xcode project for render cli util
allow setting the cache database
don't provide a default value for the stylesheet file
fix crashes when running in non-continuous mode
set rendering mode so that we can skip intermediate renders for static images
fix error in non-debug builds
don't assing nullptr to std::string
never create core profile contexts; their API is subtly different

(e.g. glGetString(GL_EXTENSIONS) doesn't work, you'd have to use glGetStringi(GL_EXTENSIONS, ...);)
automatically copy the certificate bundle
Merge pull request #718 from mapbox/cli-render

CLI render
Use iostream for saving GL program binary. Also check for GL_NUM_PROGRAM_BINARY_FORMATS > 0.
Merge pull request #729 from mapbox/shader-iostream

Use iostream for saving GL program binary + check GL_NUM_PROGRAM_BINARY_FORMATS  > 0
Merge branch 'master' of github.com:mapbox/mapbox-gl-native into android-mason

Conflicts:
	Makefile
	platform/default/headless_view.cpp
	src/mbgl/map/map.cpp
Fix lint warning