Merge branch 'master' into viewport (inc Vulkan resize fix merge #1042)

Examples: Vulkan: Passing Queue, QueueFamily to binding. Fixed scissor (fixed in master). ImGui_ImplVulkanH_DestroyWindowData() waits for device to be idle. (#1042)

Examples: DPI: Minor warning fix. (#1676)

Examples: Vulkan: Only resize swap chain and framebuffer once. (#1042)

Examples: Renamed glfw error callback for clarity.

Fixed resize window validation errors with removing frame prerender once and present last but one frame functionality. Frame rate is still similar.

Viewport, DPI: Some early work on per-viewport DPI support. At the moment the easiest way is to replace fonts during the ChangedViewport callback, but down the line we should aim at handling some of it at ImFont level. (#1542, #1676)

Examples: DPI: Portable DPI related helpers in the _Win32 examples. Using one in examples's main.cpp, the GetDpiScale functions are not wired anywhere for now. (#1542, #1676)

Viewport: Changed signature of ResizeViewport to be consistent with other similar functions.

Viewport: Coupling non-main viewport to one window. Viewport name derived from the window. Added ImGuiConfigFlags_PlatformNoTaskBar, off by default (aka re-established task-bars by default for now). (#1542)

Examples: DPI: Hacked in a quick compile-and-run-everywhere call to SetProcessDpiAwareness(), will need to revisit.

Viewport: Disable extra viewports from hosting other windows. (#1542)

Fixed warnings.

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

Examples: SDL: Fix for pre 2.0.4.

Examples: Updated Makefile and batch files to work with new examples. Using lowercase "gl.h" as it seems this is what Linux wants.

Examples: Added Makefile for SDL+OpenGL2 example. (#1668)

Examples: Added Makefile for SDL+OpenGL2 example. (#1668)

Merge branch 'master' into viewport ...

# Conflicts:
#	examples/imgui_impl_glfw.h
#	examples/opengl3_example/imgui_impl_glfw_gl3.cpp
#	examples/sdl_opengl3_example/imgui_impl_sdl_gl3.cpp
#	examples/sdl_opengl3_example/imgui_impl_sdl_gl3.h
#	imgui.cpp

Examples: OpenGL3: Added a way to override the glsl version number through the Init call. (#1667, #1466)

Merge branch 'master' into viewport ...

# Conflicts:
#	examples/allegro5_example/main.cpp
#	examples/directx10_example/main.cpp
#	examples/directx11_example/main.cpp
#	examples/directx12_example/main.cpp
#	examples/directx9_example/main.cpp
#	examples/imgui_impl_dx10.cpp
#	examples/imgui_impl_dx11.cpp
#	examples/imgui_impl_dx12.cpp
#	examples/imgui_impl_dx9.cpp
#	examples/imgui_impl_glfw.h
#	examples/imgui_impl_vulkan.cpp
#	examples/opengl2_example/imgui_impl_glfw_gl2.cpp
#	examples/opengl2_example/main.cpp
#	examples/opengl3_example/imgui_impl_glfw_gl3.cpp
#	examples/opengl3_example/main.cpp
#	examples/sdl_opengl2_example/imgui_impl_sdl_gl2.cpp
#	examples/sdl_opengl2_example/main.cpp
#	examples/sdl_opengl3_example/imgui_impl_sdl_gl3.cpp
#	examples/sdl_opengl3_example/main.cpp
#	examples/vulkan_example/main.cpp
#	imgui.cpp
#	imgui.h

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)

Examples: Vulkan: Further refactor.

Renamed ImGuiStyleVar_Count_ to ImGuiStyleVar_COUNT for consistency with other enums. Added

Examples: Vulkan: Moved CreateOrResizeWindowData func to imgui_impl_vulkan.h

Examples: Vulkan: Moved main.cpp data structures to imgui_impl_vulkan.h as shared helpers for the benefit of both the example and the platform/viewport renderer interface.

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

Examples: Vulkan: Moved variables into per-window data, refactored/tweaks to that the bug functions main.cpp for both SDL and GLFW examples match (they'll probably be moved to imgui_impl_vulkan as helpers).

Examples: Vulkan: Fix 7b968b0

Examples: Vulkan: Reduced duplicate code by skipping present on the first frame. Amend 201d589 by @ParticlePeter