Replace GLEW with a glLoadGen loader.

This should fix the GL loading errors that occur in some drivers due to
the use of deprecated functions by GLEW. Side benefits are more accurate
auto-completion (deprecated function and symbols don't exist) and faster
pointer loading (less entrypoints to load). In addition it removes an
external library depency, simplifying the build system a bit and
eliminating one set of binary libraries for Windows.

.travis-deps.sh

@@ -6,7 +6,7 @@ set -e
 if [ "$TRAVIS_OS_NAME" = linux -o -z "$TRAVIS_OS_NAME" ]; then
     sudo add-apt-repository ppa:ubuntu-toolchain-r/test -y
     sudo apt-get -qq update
-    sudo apt-get -qq install g++-4.8 xorg-dev libglu1-mesa-dev libglew-dev libxcursor-dev
+    sudo apt-get -qq install g++-4.8 xorg-dev libglu1-mesa-dev libxcursor-dev
     sudo update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-4.8 90
     git clone https://github.com/glfw/glfw.git
     mkdir glfw/build && cd glfw/build
@@ -14,5 +14,5 @@ if [ "$TRAVIS_OS_NAME" = linux -o -z "$TRAVIS_OS_NAME" ]; then
     cd -	
 elif [ "$TRAVIS_OS_NAME" = osx ]; then
     brew tap homebrew/versions
-    brew install glew qt5 glfw3 pkgconfig
+    brew install qt5 glfw3 pkgconfig
 fi