Examples: Accessing ImVector fields directly, feel less stl-ey and fix renderer side assert when render list only contains a callback (#810)

Remove local glfw3 lib for osx. (+1 squashed commit) ...

Squashed commits:
[34cc3b7] Adds osx example. (+6 squashed commits)
Squashed commits:
[20330f2] Uses glfw by brew install.
[0427861] Renames imguiex folder name to imguiex-ios
[f9e27e5] Renames ios_example to apple_example.
[44f8fe3] Updates the glfw header/library path.
[919f279] Renames target from imguiex to imguiex-ios since there is already a imguiex-osx target now.
[24395f5] Adds osx example.