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

Viewport: Popups, Tooltips can individually request no task bar icons to the platform layer. (#1542)

Viewport: Renamed RenderPlatformWindows() to RenderPlatformWindowsDefault(), tweaked examples and emphasis optional Viewport code path. (#1542)

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

IO: Added ImGuiConfigFlags_NoSetMouseCursors. Added ImGuiBackendFlags_HasMouseCursors, ImGuiBackendFlags_HasSetMousePos. (#787, #1495, #1202)

Merge branch 'master' into viewport ...

# Conflicts:
#	examples/sdl_opengl2_example/main.cpp
#	examples/sdl_opengl3_example/main.cpp
#	examples/vulkan_example/main.cpp

Examples: Renamed applications to emphasis on use of GLFW as a platform framework + minor local tweaks

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

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, Platform: SDL: Makes the CreateViewport function restore current GL context so in theory it is free from side-effect. That said, it seems like there is a bug in SDL because our CreateViewport (currently in Render(), not for long) have affect a jerky side-effect if SDL_GL_MakeCurrent() is called before Render(). (#1542)

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)

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

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

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

Renamed ImGuiStyleVar_Count_ to ImGuiStyleVar_COUNT for consistency with other enums. Added

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

Makefile: updated sdl_opengl3_example with all changes from #885.

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

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

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

ImGui_ImplSDL2_Init() now takes a SDL GL context.

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)

Merge branch 'master' into examples_refactor

Examples: SDL: Using %SDL2_DIR% in the .vcproj instead of %SDL_DIR%, the earlier is more standard.

Examples: Using SDL2_DIR instead of SDL_DIR (more standard).

Examples: OpenGL: Cast call to glPolygonMode(). (#1628).

Examples: Mouse cursor handling comments/tweaks to homogenize. (#1495)

Examples: SDL: Extracted into imgui_impl_sdl.*, reused imgui_impl_opengl* files.

Examples: SDL: Fixed minor warning.