Review description for `raygui 3.6` release!

Update examples

Update year

Update raygui.h

Fix README.md spelling: "publised" => "published" (raysan5#162)

use the same style of dll export/import definition and extern c as ra…

…ylib, so it actually works on windows. (raysan5#115)

raygui 2.6 release

GuiLabelButton() - Small tweak