Optimize _glfwInitJoysticks on OS X.

This function used to enumerate all devices and capture all properties
of every device into a dictionary. This takes 180 ms on a MacBook Pro
without external devices and 280 ms with an external keyboard/mouse
attached.

Since we're only interested in a few properties, we can just get them
one by one - this reduces the time to <1 ms.

Note that we still use the dictionary to get the joystick elements.
For unknown reason this is required to get all axes/buttons - without
doing this we don't get any joystick elements in addJoystickElement.

Closes #332.

README.md

@@ -81,6 +81,7 @@ GLFW bundles a number of dependencies in the `deps/` directory.
                    found for a given `CGDisplay`
  - [Cocoa] Bugfix: Modifier key events were lost if the corresponding modifier
                    bit field was unchanged
+ - [Cocoa] Bugfix: Joystick enumeration took hundreds of ms on some systems
  - [Win32] Enabled generation of pkg-config file for MinGW
  - [Win32] Bugfix: Failure to load winmm or its functions was not reported to
                    the error callback
@@ -160,6 +161,7 @@ skills.
  - heromyth
  - Paul Holden
  - Toni Jovanoski
+ - Arseny Kapoulkine
  - Osman Keskin
  - Cameron King
  - Peter Knut