Fixed warnings.

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

Viewport: Modal display their darkneing/whitening layer over all viewports. (#1542)

Viewport: Various sanity fixes. Popup always inherit viewport from their parent for now. (#1542)

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

Render: Removed the code that disable render if style.Alpha is 0.0f, it is both incorrect (as style Alpha can be modified mid-frame), not really necessary (just tested that full Alpha = 0 will lead to empty draw lists!) and misleading (bulk of the work was already done).

Viewport: Tracking current viewport we are appending to + added callback in PlatformInterface for DPI purpose (WIP). (#1542)

Fixed type cast warning.

Comments, FAQ update.

Columns: Fixed destructive small resize. (#1656). The OffsetNorm clamp introduced by #913 was ok as it didn't write back into the storage, which #1499 started doing making it destructive. Right now I don't think the clamp is needed at all. It had uses (eg: hide the issue fixed by bf7481e).

Columns: Extent stop at the right-most clipped pixel. The right-most column might appear a little wider but it's usable space matches the others. (#125). +9 Internal: Store InnerClipRect.

Columns: Clamping MaxX above MinX. This shouldn't have much of a benefit / affect, but the internal values are more sane this way. (#125)

Columns: Adding per-window display in Metrics. Tidying up, removing old code/comments. (#125, #1499, #1656)

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)

Renamed ImGuiStyleVar_Count_ to ImGuiStyleVar_COUNT for consistency with other enums. Added

Added ArrowButton(). Exposed ImGuiDir.

BeginCombo(): Added ImGuiComboFlags_NoArrowButton and ImGuiComboFlags_NoPreview flags + hover color matches drag and sliders.

Merge branch 'patch-1' of https://github.com/stfx/imgui into stfx-patch-1

Combo: Arrow button isn't displayed over frame color, so color is consistent with other button + the button doesn't have inner rounding.

Internal: renamed RenderTriangle() to RenderArrow().

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

Viewport: When enabled we assert against using RenderDrawListFn to make user more aware of rendering order. (#1542)

Viewport: Always be lenient with invalid mouse position during dragging, since they are provided by back-end and technically acceptable inputs + comments. (#1542)

Nav: Added links to PNG/PSD files for PS4 and Switch. Fixed suggested Joy-con mapping as per typical Nintendo-style mapping. (#787)

Internal: Moved IM_NEWLINE helper to imgui_internal.h

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

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

Viewport: Initial viewport branch+ platform api commit (squashed from previous commits, still very WIP) (#1542)

Metrics: Added option to show begin order, useful for debugging.