[examples] raylib 2.5 Web examples review

[raysan5]

Current examples collection (96 examples) have been adapted, compiled and tested on web using raylib 2.5. Some examples are not working properly, here a list with the issues:

• core/core_drop_files : not working
• core/core_loading_thread : errors on thread creation
• textures/textures_image_text : glReadPixels: invalid format -> Not used any more
• textures/textures_to_image : glReadPixels: format and type incompatible
• models/models_skybox : shaders not supported on glsl100 > SKIP
• models/models_materials_pbr: : shaders not supported on glsl100 > SKIP
• shaders/shaders_palette_switch : shader not supported on glsl100
• shaders/shaders_raymarching : shader not supported on glsl100 > SKIP
• shaders/shaders_texture_drawing : shader not supported on glsl100
• shaders/shaders_erastosthenes : shader not supported on glsl100
• physac/physics_demo : errors on thread creation
• physac/physics_friction : errors on thread creation
• physac/physics_movement : errors on thread creation
• physac/physics_restitution : errors on thread creation
• physac/physics_shatter : errors on thread creation

Any help with those issues is welcome.

[raysan5]

Update on web examples:

Multithreading examples seem to compile again but for some reasons they do not work properly:

• core/core_loading_thread > Local thread variables were not working on thread conditions (yes, very weird) and on physac examples physic steps are not running.
• physac/physics_* > GetCurrentTime() not working on web, physics must be called on main thread using PhysicsStep(). Maybe this module should be redesigned to leave physics update control to user.

[raysan5]

• core/core_drop_files not working was tracked down to emscripten library_glfw.js, here the related issue [src/library_glfw.js] onDrop event not processed emscripten-core/emscripten#10004

[raysan5]

• textures/textures_to_image reviewed by commits e614942 and 03e6006