BeginTabBar: Fix to push the expected ID into the ID stack (instead of a hash's hash). (#261)

Added BETA api for Tab Bar/Tabs widgets. (#261, #351) (merged this feature from the from Docking branch so it can be used earlier as as standalone feature) ...

- Added BeginTabBar(), EndTabBar(), BeginTabItem(), EndTabItem(), SetTabItemClosed() API.
- Added ImGuiTabBarFlags flags for BeginTabBar().
- Added ImGuiTabItemFlags flags for BeginTabItem().
- Style: Added ImGuiCol_Tab, ImGuiCol_TabHovered, ImGuiCol_TabActive, ImGuiCol_TabUnfocused, ImGuiCol_TabUnfocusedActive colors.
- Demo: Added Layout->Tabs demo code.
- Demo: Added "Documents" example app showcasing possible use for tabs.

Using named flags instead of 0 + shallow formatting tweaks from other branches.

Tests: Adding imgui-test engine hooks (experimental) to provide missing widget state to the testing system.

Internals: Nav: Added ImGuiNavLayer_ to clarify semantic of previously integer NavLayer values, and not pretend that increment/decrement operators on them super flexible. + Storage tweaks.

Version 1.67 WIP (again, this time IMGUI_VERSION_NUM has leeway for another hot-fix).

Version 1.66b (will revisit how to change IMGUI_VERSION_NUM across versions, this commit reduces the numerical IMGUI_VERSION_NUM compared to the commit on Nov 22).

Separator: Fixed Separator() outputting an extraneous empty line when captured into clipboard/text/file.

Version 1.67 WIP

Version 1.66

Internals: DragBehavior: Added support for ImGuiDragFlags_Vertical to implement a vertical drag widget (no frontend function provided).

Internals: SliderBehavior: Using axis indexing.

ListBox(): Fixed frame sizing when items_count==1 unnecessarily showing a scrollbar. (#2173). Tweaked frame sizing so list boxes will look more consistent when FramePadding is far from ItemSpacing.

Internals: Moved the FocusableItemUnregister() outside of InputScalarAsWidgetReplacement(), it should not be here and doesn't facilitate reusing InputScalarAsWidgetReplacement(). (cc #2155)

SliderAngle: Added optional `format` argument to allow users customize precision and make localization. (#2150)

Removed unnecessary ImGui:: qualifiers in internal code.

Revert using wchar_t functions (9cf94d5 + 2eaf5b0). Big mistake, wchar_t is not guaranteed to be 16-bits.

Fixes crash introduced in previous commit 9cf94d5.

RenderText(), InputTextMultiline(): Optimization for large text by using memchr, wmemchr, wcschr when appropriate.

Renamed misc/stl/imgui_stl.h,.cpp to misc/cpp/imgui_stdlib.h in prevision for other files.(#2035, #2096) ...

Added misc/README file.

TextUnformatted: Using memchr(), fixed not properly testing for text_end bound + comments. ...

Internals: Added ImStreolRange() + used in LogRenderedText() + comments.

ArrowButton(): Fixed arrow shape being horizontally misaligned by (FramePadding.y-FramePadding.x) if they are different. ...

Demo: Added extra usage of AlignTextToFramePadding() in a more visible section.

BeginMenu(): Fixed menu popup horizontal offset being off the item in the menu bar when WindowPadding=0.0f.

ColorPicker: Replaced the Separator with a Spacing call. (#2068)

Fix MSVC's C4312 warning about casting user texture type to void* in ImageButton (#2080)

Internals: Replace unsigned short with ImWchar when dealing with character storage (missing cases) + in imgui_impl_ file keep using neutral type everywhere, added missing explicit cast in three bindings. (#2078)

DragFloat: Disabled using power curve when one edge is FLT_MAX (broken in 1.61). Disabled setting a default drag speed when one edge is FLT_MAX. (#2024)

DragFloat: Fixed a situation where dragging with value rounding enabled or with a power curve erroneously wrapped the value to one of the min/max edge. (#2024, #708, #320, #2075).

Nav, Focus: Fixed ImGuiWindowFlags_NoBringToFrontOnFocus windows not being restoring focus properly after the main menu bar or last focused window is deactivated.

Version 1.66 WIP