Doc: removed "generic" docking/viewport branch section of changelog s…

…ince this is misleading. Will add formally when we reelase. (#2109, #1542)

docs/CHANGELOG.txt

@@ -30,72 +30,6 @@ HOW TO UPDATE?
   and API updates have been a little more frequent lately. They are documented below and in imgui.cpp and should not affect all users.
 - Please report any issue!
 
------------------------------------------------------------------------
- DOCKING+MULTI-VIEWPORT BRANCH (In Progress)
------------------------------------------------------------------------
-
-DOCKING FEATURES
-(see https://github.com/ocornut/imgui/wiki/Docking for quick intro)
-
-- Added Docking system: [BETA] (#2109, #351)
-  - Added ImGuiConfigFlags_DockingEnable flag to enable Docking.
-    Set with `io.ConfigFlags |= ImGuiConfigFlags_DockingEnable;`.
-  - Added DockSpace(), DockSpaceOverViewport() API.
-  - Added ImGuiDockNodeFlags flags for DockSpace().
-  - Added SetNextWindowDockID(), SetNextWindowClass() API.
-  - Added GetWindowDockID(), IsWindowDocked() API.
-  - Added ImGuiWindowFlags_NoDocking window flag to disable the possibility for a window to be docked.
-    Popup, Menu and Child windows always have the ImGuiWindowFlags_NoDocking flag set.
-  - Added ImGuiWindowClass to specify advanced docking/viewport related flags via SetNextWindowClass().
-  - Added io.ConfigDockingNoSplit option.
-  - Added io.ConfigDockingWithShift option.
-  - Added io.ConfigDockingAlwaysTabBar option.
-  - Added io.ConfigDockingTransparentPayload option.
-  - Style: Added ImGuiCol_DockingPreview, ImGuiCol_DockingEmptyBg colors.
-  - Demo: Added "DockSpace" example app showcasing use of explicit dockspace nodes.
-
-MULTI-VIEWPORT FEATURES
-(see https://github.com/ocornut/imgui/wiki/Multi-Viewports for quick intro)
-
-Breaking Changes:
-
-- IMPORTANT: When multi-viewports are enabled (with io.ConfigFlags |= ImGuiConfigFlags_ViewportsEnable),
-  all coordinates/positions will be in your natural OS coordinates space. It means that:
-   - Reference to hard-coded positions such as in SetNextWindowPos(ImVec2(0,0)) are _probably_ not what you want anymore.
-     Use GetMainViewport()->Pos to offset hard-coded positions, e.g. SetNextWindowPos(GetMainViewport()->Pos).
-   - Likewise io.MousePos and GetMousePos() will use OS coordinates.
-     If you query mouse positions to interact with non-imgui coordinates you will need to offset them.
-     e.g. subtract GetWindowViewport()->Pos.
-- IO: Removed io.DisplayVisibleMin, io.DisplayVisibleMax settings (they were marked obsoleted, used to clip within the (0,0)..(DisplaySize) range).
-
-Other changes:
-(FIXME: This need a fuller explanation!)
-
-- Added ImGuiPlatformIO structure and GetPlatformIO().
-  - Similarly to ImGuiIO and GetIO(), this structure is the main point of communication for backends supporting multi-viewports.
-  - Backend sets functions in ImGuiPlatformIO to manipulate platform windows.
-  - ImGuiPlatformIO::Monitors is a list of platform monitors (input from backend)
-  - ImGuiPlatformIO::Viewports is a list of viewports (output from dear imgui)
-- Added ImGuiPlatformMonitor to feed OS monitor information in the ImGuiPlatformIO::Monitors.
-- Added GetWindowViewport(), SetNextWindowViewport().
-- Added GetWindowDpiScale().
-- Added GetOverlayDrawList(ImGuiViewport* viewport).
-  The no-parameter version of GetOverlayDrawList() return the overlay for the current window's viewport.
-- Added UpdatePlatformWindows(), RenderPlatformWindowsDefault(), DestroyPlatformWindows() for usage in application setup.
-- Added FindViewportByID(), FindViewportByPlatformHandle() for usage by backends.
-- Added ImGuiConfigFlags_ViewportsEnable configuration flag and other viewport options.
-- Added io.ConfigViewportsNoAutoMerge option.
-- Added io.ConfigViewportsNoTaskBarIcon option.
-- Added io.ConfigViewportsNoDecoration option.
-- Added io.ConfigViewportsNoDefaultParent option.
-- Added ImGuiBackendFlags_PlatformHasViewports, ImGuiBackendFlags_RendererHasViewports, ImGuiBackendFlags_HasMouseHoveredViewport backend flags.
-- Added io.AddMouseViewportEvent() (optional _even_ for multi-viewport support, tied to ImGuiBackendFlags_HasMouseHoveredViewport flag).
-- Expanded ImGuiViewport structure, ImGuiViewportFlags flags.
-- Added ImGuiWindowClass and SetNextWindowClass() for passing viewport related hints to the OS/platform back-end.
-- Examples: Renderer: OpenGL2, OpenGL3, DirectX9, DirectX10, DirectX11, DirectX12, Vulkan: Added support for multi-viewports.
-- Examples: Platforms: Win32, GLFW, SDL2: Added support for multi-viewports.
-  Note that Linux/Mac still have inconsistent support for multi-viewports. If you want to help see https://github.com/ocornut/imgui/issues/2117.
-
 
 -----------------------------------------------------------------------
  VERSION 1.89.8 WIP (In Progress)