Examples: Fixes.

Merge branch 'master' into viewport ...

# Conflicts:
#	examples/imgui_impl_glfw.cpp
#	examples/imgui_impl_win32.cpp

Examples: DirectX12: Moved the ID3D12GraphicsCommandList* parameter from ImGui_ImplDX12_NewFrame() to ImGui_ImplDX12_RenderDrawData() which makes a lots more sense. (#301)

Merge branch 'master' into viewport ...

# Conflicts:
#	examples/imgui_impl_dx10.cpp
#	examples/imgui_impl_dx10.h
#	examples/imgui_impl_dx11.cpp
#	examples/imgui_impl_glfw.cpp
#	examples/imgui_impl_glfw.h
#	examples/imgui_impl_opengl2.cpp
#	examples/imgui_impl_opengl2.h
#	examples/imgui_impl_opengl3.cpp
#	examples/imgui_impl_sdl.cpp
#	examples/imgui_impl_sdl.h
#	examples/imgui_impl_vulkan.h
#	examples/imgui_impl_win32.cpp

Examples: Comments to make ImGuiConfigFlags_NoMouseCursorChange more visible (#1027). + Allegro5: Added support for ImGuiConfigFlags_NoMouseCursorChange flag.

Merge branch 'examples_refactor2' into viewport (#1870) ...

# Conflicts:
#	examples/README.txt
#	examples/directx11_example/main.cpp
#	examples/directx12_example/main.cpp
#	examples/imgui_impl_dx10.cpp
#	examples/imgui_impl_dx11.cpp
#	examples/imgui_impl_dx12.cpp
#	examples/imgui_impl_glfw.cpp
#	examples/imgui_impl_opengl2.cpp
#	examples/imgui_impl_opengl2.h
#	examples/imgui_impl_opengl3.cpp
#	examples/imgui_impl_sdl2.cpp
#	examples/imgui_impl_sdl2.h
#	examples/imgui_impl_vulkan.cpp
#	examples/imgui_impl_vulkan.h
#	examples/imgui_impl_win32.cpp
#	examples/imgui_impl_win32.h
#	examples/opengl2_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.cpp
#	imgui.h

Big example binding refactor (manually imported from Viewport branch, stripped out of Viewport code). (#1870) ...

Read examples/README.txt for some details.
ImDrawData: Added DisplayPos, DisplaySize fields honored by all backends (not strictly necessary to honor just now, but doing it to be ahead)

Viewport: Fixed mouse hover flicker on mouse button release frame after moving a window. (#1542) ...

Platform: Clarifying some comments in back-ends.

Viewport, Platforms: SDL: Fixed initial focus click being ignored as a mouse button. GLFW: Fixed mouse cursor support for multi-viewport with GLFW 3.3 (current master) - somehow doesn't appear to work with GLFW 3.2 but I'm not too fussed about it. (#1542)

Viewports, DPI: Renamed config flags. (#1542)

Examples, Platform, Viewport: Fixed inconsistent window ownership issues. Added comments. Made Win32/SDL back-ends track ownership.

Merge branch 'master' into viewport ...

# Conflicts:
#	examples/imgui_impl_dx10.cpp
#	examples/imgui_impl_dx11.cpp
#	examples/imgui_impl_dx12.cpp
#	examples/imgui_impl_dx9.cpp
#	examples/opengl2_example/imgui_impl_glfw_gl2.cpp
#	examples/opengl3_example/imgui_impl_glfw_gl3.cpp
#	examples/sdl_opengl2_example/imgui_impl_sdl_gl2.cpp
#	examples/sdl_opengl3_example/imgui_impl_sdl_gl3.cpp
#	examples/vulkan_example/imgui_impl_glfw_vulkan.cpp
#	imgui.h

Viewport, Platform: Added void* to render/swap buffer functions. Comments. (#1542, #1042)

Viewport, Examples: Renamed types used by examples. (#1542)

Viewport, Platform: Refactored platform interface. Removed need to use imgui_internal.h in backends. Split viewport into public facing ImGuiViewport and internal structure. Exposing enough data to provide custom tweaked renderers. Renamed handlers, fixed lots of inconsistencies. (#1542, #1042)

Viewport: Removed back-end renderer code that implied we need to clear with WindowBg color. Added NoRendererClear flag. (#1542, #1042)

Viewport: Reorganized viewport enable flags. Both user + platform + renderer need to enable a flag. (#1542)

Viewport: Give a chance to platform and renderer to actually destroy their data. Otherwise the regular ImplXXX_Shutdown + following by DestroyContext() order fails to fullifl this. (#1542)

Viewport: Replaced UpdatePlatformWindows/RenderPlatformWindows by RenderAdditionalViewports(). The update is always called in EndFrame(). (#1542)

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

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