Examples: Vulkan: Various tweak. Misc refactor into per-frame data. Duplicate buffer creation code moved to CreateOrResizeBuffer().

Examples: GLFW, Vulkan: GLFW binding viewport tweaks to supports Vulkan better (do not call SwapBuffer, share context etc.). Added DUMMY (empty) platform/viewport interface in the viewport code.

Examples: Renamed glfw error callback so it's more clear what it is.

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.

Makefile: updated sdl_opengl3_example with all changes from #885.

Do not store compiled objects outside the project tree.

Define SOURCES instead of OBJS in Makefiles. ...

OBJS is still deduced from SOURCES, but this change gives better control
over where the object files get actually written.

Use make variables $@ and $^ where appropriate.

Ensure `make clean` is idempotent. ...

Prior to this, `make clean` would fail if the project was not already
fully built, and a second invokation would always fail.

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

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

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

Examples: DX10: Multi viewport/platform support (based on DX11 version). (#1542)

Examples: NULL pointers for consistency.

Examples: DX12: Empty skeleton toward implementing the multi-viewport api for DirectX12. (WIP/test API) (#1542, #301)

Examples: SDL: Initial attempt at implementing the viewport/platform api. (WIP/test API) (#1542) ...

ImGui_ImplSDL2_Init() now takes a SDL GL context.

Examples: GLFW + OpenGL3: Initial attempt at implementing the viewport/platform api. (WIP/test API) (#1542)

Examples: DX11 + Win32: Initial attempt at implementing the viewport/platform api. (WIP/test API) (#1542)

Examples: Misc tweaks/fixes.

Merge branch 'master' into examples_refactor ...

# Conflicts:
#	examples/opengl3_example/imgui_impl_glfw_gl3.cpp
#	examples/sdl_opengl3_example/imgui_impl_sdl_gl3.cpp

Examples: Fix d749d49 missing the deletion code. (#1217)

Examples: OpenGL3: Create the VAO in the render function so the setup can more easily be used with multiple shared GL context. (#1217)

Examples: DirectX12: Merged to new example format, imgui_impl_dx12.cpp contains the DX12 stuff, couple with imgui_impl_win32.cpp

Merge branch 'master' into examples_refactor

Examples: DirectX12: Tweaked assertion to more accurately represent what it wants to say. (#301)