Merge branch 'examples_refactor' into viewport ...

# Conflicts:
#	examples/directx10_example/main.cpp
#	examples/directx11_example/main.cpp
#	examples/directx12_example/main.cpp
#	examples/opengl3_example/main.cpp
#	examples/sdl_opengl2_example/main.cpp
#	examples/sdl_opengl3_example/main.cpp
#	examples/sdl_vulkan_example/main.cpp
#	examples/vulkan_example/main.cpp
#	imgui.h

Examples: Vulkan: SDL: Fixed missing resize handler (not properly merged from #1367) + tweaks.

Examples: Vulkan: Moved code into shared helpers: ImGui_ImplVulkan_SelectSurfaceFormat, ImGui_ImplVulkan_SelectPresentMode.

Examples: Vulkan: Various tweaks to name variable more consistently like Vulkan + a few comments + a few imgui style code compaction.

Examples: Vulkan: Debug report tweak + always enable in Debug build.

Examples: Fixed enabling IMGUI_VULKAN_DEBUG_REPORT which was broken during refactor because of duplicate 'extensions' local variable.

Renamed ImGuiNavFlags io.NavFlags to ImGuiConfigFlags io.ConfigFlags. (#787)

Renamed ImGuiNavFlags io.NavFlags to ImGuiConfigFlags io.ConfigFlags. (#787)

Examples: NULL pointers for consistency.

Examples: Vulkan: Formatting and tweaks (to match SDL's main).

Examples: Vulkan: Fixed GLFW calls.

Examples: Vulkan: Extracted into imgui_impl_vulkan.*, reused imgui_impl_glfw* files.

Examples: Vulkan: Fix for empty draw data (init time) + fixed warning.

Merge branch 'context' ...

# Conflicts:
#	examples/allegro5_example/main.cpp
#	examples/directx10_example/main.cpp
#	examples/directx11_example/main.cpp
#	examples/directx9_example/main.cpp
#	examples/marmalade_example/main.cpp
#	examples/opengl2_example/main.cpp
#	examples/opengl3_example/main.cpp
#	examples/sdl_opengl2_example/main.cpp
#	examples/sdl_opengl3_example/main.cpp
#	examples/vulkan_example/main.cpp

Nav: Examples: Added commented out io.NavFlags |= ImGuiNavFlags_EnableKeyboard to all examples. (#787)

Merge branch 'master' into context

Moved extra_fonts/ to misc/fonts/. Moved .natvis file to misc/natvis/ (#1569)

Examples: Using Dark theme by default. (#707). Tweaked demo code.

Examples: Using #include "imgui.h" instead of <imgui.h> appear correct-er as per standard? xcode+clang are very nitpicky there.

Examples: Updated for reorganized context functions. Calling CreateContext(), DestroyContext() in example code. Removed Shutdown() from binding code. (#1565, #586, #992, #1007, #1558)

Examples: Vulkan: Tweak

Examples: Comments, synched some minor drift between examples + stronger suggestion to use StyleColorsDark().

Renamed the emblematic ShowTestWindow() function to ShowDemoWindow(). Kept redirection function (will obsolete).

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: 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()

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

Examples: Vulkan: Various very minor stylistic fixes, fixing typos in comments, etc. (#1042 #1043)