GLEW should be replaced

[milesrout]

GLEW has several annoying bugs and issues with binary builds. We should replace it with a different extension loader, for example gl3w or glad.

[ghost]

http://glad.dav1d.de/

[adam4813]

GLFW3 has a glad backend.

[milesrout]

For reference, all files that contain 'glew':

miles@laptop:~/Projects/trillek/tec $ grep -Rie 'glew' . | grep -v './modules' | grep -v './build'
Binary file ./.git/index matches
./.travis.yml:                  - libglew-dev
./.travis.yml:                  - libglew-dev
./appveyor.yml:- mkdir glew
./appveyor.yml:- nuget install rxd_glew -o c:\projects\glew
./appveyor.yml:- set PATH=%PATH%;c:\projects\glew
./appveyor.yml:- 'copy c:\projects\glew\rxd_glew.1.10.0.1\build\native\lib\Win32\v120\dynamic\*.lib '
./appveyor.yml:- copy c:\projects\glew\rxd_glew.1.10.0.1\build\native\lib\Win32\v120\static\*.lib c:\projects\tec\lib\
./appveyor.yml:- xcopy /E c:\projects\glew\rxd_glew.1.10.0.1\build\native\include c:\projects\tec\lib\include\
./AUTHORS.txt:*modules/FindGLEW.cmake
./client/graphics/gbuffer.hpp:#include <GL/glew.h>
./client/graphics/lights.hpp:#include <GL/glew.h>
./client/graphics/material.hpp:#include <GL/glew.h>
./client/graphics/shader.hpp:#include <GL/glew.h>
./client/graphics/texture-object.hpp:#include <GL/glew.h>
./client/graphics/vertex-buffer-object.hpp:#include <GL/glew.h>
./client/imgui-system.hpp:#include <GL/glew.h>
./client/imgui-system.hpp:#include <GL/wglew.h>
./client/render-system.hpp:#include <GL/glew.h>
./CMakeLists.txt:IF (NOT APPLE) # X11 and GLEW are not needed on OSX.
./CMakeLists.txt:  FIND_PACKAGE(GLEW REQUIRED) # We find GLEW here as OSX doesn't need it.
./CMakeLists.txt:  SET(GLEW_LIBRARY "") # Set a dummy value for GLEW.
./CMakeLists.txt:    ${GLEW_LIBRARIES}
./include/os.hpp:#include <GL/glew.h>
./include/os.hpp:#include <GL/wglew.h>
./README.md:TEC requires cmake 3.1 and a few libraries like GLEW, Lua, Bullet and OpenAL. Our CMake script can handle compiling and installing Bullet and OpenAL, but GLEW and Lua is necesary to be installed on your computer to build the engine properly.
./README.md:     - If you have Bullet, GLEW and OpenAL dev libs installed : 
./README.md:- Glew : Use nuget -> nuget install rxd_glew 
./README.md:- **OR** for prebuilt (lua5.2 and glew lib files) download https://www.dropbox.com/s/m7vzruxrq8f79zo/tec_win32_libs.zip?dl=0 and extract it into the root repo folder.
./src/os.cpp:           // setting glewExperimental fixes a glfw context problem
./src/os.cpp:           glewExperimental = GL_TRUE;
./src/os.cpp:           // Init GLEW.
./src/os.cpp:           GLuint error = glewInit();
./src/os.cpp:           if (error != GLEW_OK) {
./src/os.cpp:        wiki, some version of GLEW generate a GL_INVALID_ENUM when
./src/os.cpp:        glewInit() is called which can be safely ignored. Do not remove

[milesrout]

this can wait for the next major release

[adam4813]

Some _EXT are no longer present as is, I had to search through https://raw.githubusercontent.com/Dav1dde/glad/master/glad/files/gl.xml to see the alias