+ fixed PVS warning, update demo binaries, update readme image

Backends: OpenGL3: Fixed version check mistakenly testing for GL 4.0+ instead of 3.2+ to enable ImGuiBackendFlags_RendererHasVtxOffset, leaving 3.2 contexts without it. (#3119, #2866, #2852)

Internals: Extracted GetWindowScrollbarRect() out of Scrollbar() and tidying up code to make it more obvious how to draw over scrollbars. (#3114)

Made default clipboard handlers for Win32 and OSX use a buffer inside the main context instead of a static buffer, so it can be freed properly on Shutdown. (#3110)

Regretfully moved .gitignore file from examples/ into root directory because OSX keeps pooping its DS_Store/ artifacts everywhere. (#3088)

Backends: Comments next to include, misc minor comments/tweaks, fix imgui_impl_osx.h using IMGUI_API instead of IMGUI_IMPL_API. (#3105)

Currently, the implementation headers don't include the imgui.h header.
Which means that the compilation will fail if the implementation header
was included before the imgui.h header in the compilation unit. For
instance, a compilation unit with the following will work:

  #include "imgui.h"
  #include "imgui_impl_glfw.h"
  #include "imgui_impl_opengl3.h"

But a compilation unit with the following will fail because IMGUI_IMPL_API
and possibly other symbols will not be defined:

  #include "imgui_impl_glfw.h"
  #include "imgui_impl_opengl3.h"
  #include "imgui.h"

This patch includes imgui.h in the implementation headers to make
inclusions order-invariant, which is a recommended practice.

Misc: Added an explicit compile-time test for non-scoped IM_ASSERT() macros to redirect users to a solution + fixed our stb wrappers.

+ Nav: Use nav layer enum, comments.

Columns: undid the change in 1.75 were Columns()/BeginColumns() were preemptively limited to 64 columns with an assert. (#3037, #125)

Essentially reverting 9d444062.

+ renamed NavScoringRectScreen > NavScoringRect

TreeNode: Made clicking on arrow with _OpenOnArrow toggle the open state on the Mouse Down  event rather than the Mouse Down+Up sequence (this is rather standard behavior).

Selectable: Allow using ImGuiSelectableFlags_SpanAllColumns in other columns than first. Comments. (#125)

Selectable: Removed extraneous WindowPadding.x worth of width when auto-sized selectable label goes off available width (would not be noticeable) + Renamed ImGuiSelectableFlags_DrawFillAvailWidth to ImGuiSelectableFlags_SpanAvailWidth.

Selectable: Clarifying the code around use of ImGuiSelectableFlags_DrawFillAvailWidth (with intent of trying to remove it).

Amend old 6251d379, 2bcafc86

Selectable: Removed seemingly ineffective text clipping offset in SpanAllColumns handling path + tweaks.

made max_x absolutely to reduce confusion.
amend cf481e1a

Added IMGUI_USE_WCHAR32 instead of "#define ImWchar ImWchar32" to faclitate C-binding. (#2538, #2541, #2815)

This removes the unversioned definition IMGUI_IMPL_OPENGL_LOADER_GLBINDING in favor of two versioned ones to choose explicitly.
References: #2870, 5e2329b9

Scrolling: Fixed scrolling centering API leading to non-integer scrolling values and initial cursor position. (#3073)

This would often get fixed after the fix item submission, but using the ImGuiListClipper as the first thing after Begin() could largely break size calculations. (#3073)

Added ImGuiKeyModFlags. Added additional checks in EndFrame() to verify that io.KeyXXX values have not been tampered with between NewFrame() and EndFrame().

Internal: Refactor: Moved RenderColorRectWithAlphaCheckerboard() to imgui_draw.cpp, tweaked signature.

Internal: Refactor: Moved RenderArrow, RenderBullet, RenderCheckMark to imgui_draw.cpp, changed RenderCheckMark to avoid using ImGui context

Copies the #define magic from imgui_draw.cpp to the imgui_freetype implementation to allow the use of a custom stb rect_pack here as well.
References: fe5347ef

+ amend notes

Internals: Renamed ImBoolVector to ImBitVector, added low-level loose function to replicate the behavior include a help SetBitRange() function.

ImVec2 *= ImVec2 to match  ImVec2 * ImVec2, likewise with /