Sisyphus says: tweaked comments about not using old-style OpenGL examples (#1459, #1394 etc.)

Examples: Added a bunch of comments/referencs related to io.WantCaptureMouse, io.WantCaptureKeyboard (#1262, #1237, #1219, #635, #1058, #1051, #912, #533, #703, #446, #459, #364, #213, #52, and more)

Examples: Comments to guide people unfamiliar with the librairies used.

Examples: Added more comments near the fonts loading section, to catch common questions and errors (e.g. #1397, #1366, #1341, #1222, #1193, #1115, #951, etc.)

Examples: Adding Roboto to the commented-out font list, and removing the unnecessary ProggyClean from there.

Examples: Avoid using ImColor() to not tempt newcomers into looking at it

Examples: Main: Removed call to SetNextWindowSize()

Examples: GL2: rename functions to include GL2 in name

Renamed ImGuiSetCond_XXX type and enums to ImGuiCond_XXX, kept old enums under #ifdef IMGUI_DISABLE_OBSOLETE_FUNCTIONS

Examples: Enable vsync by default in example applications (#1213, #1151)

Examples: OpenGL2+GLFW/SDL: Added commented out glUseProgram(0) in main.cpp for visibility (#1116)

Examples: Renaming opengl_example/ to opengl2_example/ for clarity (1/2 because git)