Merge branch 'master' into viewport ...

# Conflicts:
#	imgui.cpp
#	imgui_internal.h

Viewport: per-viewport overlay draw list created on demand. With this pattern it'll be easier to consider adding more (e.g. background draw list). (#545)

Internals: Popup: Moved popup/menu/tooltip positioning code (viewport branch needs it organized in a different manner, so we are pushing the bulk of it here to minimize differences).

Internals: Window: Aggregating ImDrawList into the ImGuiWindow structure.

Settings: Fixed saving an empty .ini file if CreateContext/DestroyContext are called without a single call to NewFrame(). (#1741)

NewFrame: Prevent division by zero in frame rate calculation if io.DeltaTime is continuously zero. (#1740, #881)

Viewport: Merged ImGuiPlatformData into ImGuiPlatformIO. Comments. (#1542)

Viewport, Platform: Added a way to register monitor bounds to imgui so they can be used to clamp individual-viewport tooltips/popups so they don't straddle monitors. (#1542)

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

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

Viewport: shuffled some code in the UpdateSelectWindowViewport() function.

Begin: moved tooltip position code in an else block. Misc comments

Internals: Renamed GetFrontMostModalRootWindow() to GetFrontMostPopupModal() and exposed in imgui_internal.h (#1738)

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

Misc: IM_DELETE() helper function added in 1.60 doesn't clear the input _pointer_ reference, more consistent with expectation and allows passing r-value.

Merge branch 'master' into viewport ...

# Conflicts:
#	examples/imgui_impl_dx10.cpp
#	examples/opengl2_example/imgui_impl_glfw_gl2.cpp
#	examples/opengl3_example/imgui_impl_glfw_gl3.cpp
#	examples/vulkan_example/main.cpp
#	imgui.h

Version 1.61 WIP

Version 1.60

Internals: Removed unused internal variant of ArrowButton().

Fixed a few zealous warnings.

Fixed unused variable warning.

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.cpp
#	imgui.h
#	imgui_internal.h

Style: Default style is now StyleColorsDark()! Toward a 1.60 release :) (#707)

IO: ImGuiConfigFlags_NoMouse disable hovering so it is not destructive. Amend 2464e62

NewFrame: Extract some code into a NewFrameUpdateHoveredWindowAndCaptureFlags() which can be of use with touch-based inputs systems.

Comments about io.WantCapture flags + todo entries.

NewFrame: Extract some code into a NewFrameUpdateMouseInputs function. Moved settings saving higher up in the function so it is next to its peers.

IO: Added ImGuiConfigFlags_NoMouse to force clear/disable mouse inputs in NewFrame().

Columns: Fixed calling Columns() again with the same number of columns. (#125)

Viewport, Platform, Examples: Added support for transparent window via PlatformIO Platform_SetWindowAlpha (#1542) + fixes for GLFW 3.3