Revert "Assert that fmt != NULL before calling vsnprintf (#1969)" ...

This reverts commit 84183f5.

Speculative va_copy() fix for old versions of GCC/Clang. (cannot repro) (#1085)

Visual Studio: calling into _vsnprintf. (#1085)

Internals: Fixed HoveredIdTimer so it is safe to call SetHoveredId() multiple times without altering the timer.

CollapseButton: Added hovering highlight + minor consistency tweaks.

Internals: Drag and Drop: default drop preview use a narrower clipping rectangle (no effect here, but other branches uses a narrow clipping rectangle that was too small so this is a fix for it) + Comments

Internals: Changed SplitterBehavior() signature to be consistent with other similar signatures. (#319).

Internals: Extracted part of Begin into UpdateWindowParentAndRootLinks(). Useful to call to keep state updated immediately (namely useful for docking) + small tidying up of imgui_internal.h

Assert that fmt != NULL before calling vsnprintf (#1969) ...

In the case of Visual Studio 15.6 + Windows SDK 10.0, vsnprintf() with NULL format string appears to corrupt the stack...

Internals: Child windows that are clipped or part of a collapsed parent are not marked as collapsed anymore, but just a separate hidden marker set. We distinguish hiding for size measurement vs hiding for other reasons. Cleaned a little the end of Begin.

Nav: Tweaked CTRL+TAB to hide visual noise on fast switch + fading out screen dimming and highlight to make the experience less harsh

FAQ update

Internals: SplitterBehavior() added hover_visibility_delay parameter which is helpful to reduce visual noise. (#319)

Made it possible to move a window by dragging from the Collapse button (past the drag threshold). Extracted some code out to a CollapseButton() function.

Internals: Renamed one of the arrow functions so their name don't collide.

Fixed horizontal mouse wheel not forwarding the request to the parent window if ImGuiWindowFlags_NoScrollWithMouse is set. (#1463, #1380, #1502)

Internals: Extracted part of NewFrame() into a UpdateMouseWheel() function.

Added asserts to catch illegal modifications of the font atlas between NewFrame() and EndFrame()/Render(). (#1958)

Changed ImGui::GetTime() return value from float to double to avoid accumulating floating point imprecisions over time.

ImGuiTextFilter, TextRange: removed cruft from TextRange since it's not a publicly and generic helper at the moment + marked internal stuff + changed a reference to a pointer. (#1879)

Nav: Fixed CTRL+TAB windowing list from always showing the implicit Debug window. (#787)

Fix warning when IMGUI_DEFINE_MATH_OPERATORS is already defined by build system. (#1950)

Comments, exposed a few things in imgui_internal.h for consistency, added ImQsort wrapper.

Revert part of c7016c2 incorrectly renaming ImGuiCol_NavWindowingHighlight to ImGuiCol_NavWindowListHighlight, that was wholly unnecessary (and not documented!). (also invalidate #1939)

IsItemHovered(): Added ImGuiHoveredFlags_AllowWhenDisabled flag to query hovered status on disabled items. (#1940, #211) ...

+ shallow changelog tweaks

Fixed missing value in GetStyleColorName(). (#1939) broken with c7016c2

Internals: Extracted StartMouseMovingWindow so we can add code to turn an arbitrary widget into a window mover (will be useful to make the Collapse button a window mover past a mouse drag threshold) + added a couple of _None flags.

Internals: Fixed CalcSizeContents() returning negative value on first run (inconsequential afaik, but fixing for sanity)

Internals: Misc/shallow merge from Docking branch.

Internals: Move IMGUI_CDECL declaration to imgui_internal.h so everyone can profit.