[examples] Some new examples proposed

[raysan5]

Here it is a small list of new examples that I think could be interesting for raylib. If anyone wants to work on any of them, please, make sure to follow examples_template. Please, try to make examples a bit appealing for the user! :)

• core_scissor_test : Functionality was added in raylib 2.5 but no usage example provided yet.
• textures_cubemap : Functionality was added in raylib 2.5 but no usage example provided yet. LoadTextureCubemap() processes an input image (multiple layouts supported) and returns a cubemap texture... some additional function could be needed to draw the TextureCubemap...
• textures_mouse_painting : Canvas painting demo with mouse, for example LMB to paint and RMB to erase, with some basic color selection options.
• shaders_basic_lighting : Basic phong lighting samples, this one is almost ready to be added! (81d8302)
• shaders_fog_effect : Basic fog (configurable?) using a shader, it can be combined with a heightmap for usage (4b79f63).

Alternatively, there are several examples that require some review, view #847 and #851.

[chriscamacho]

scissor mode would be more useful if the view port could be changed too, however this impacts functions like GetMouseRay which currently assume a fullscreen viewport...

[raysan5]

@ChrisDill reviewed your examples on commit 602d2a6. Take a look! ;)

[chriscamacho]

gaaah if statements without braces.... @raysan5 they hurt my eyes :-p

[rgebee]

@raysan5 Thanks! The changes look really good! :)

[raysan5]

Closing this issue for now.