Viewport: Added ImGuiConfigFlags_ViewportsDecoration to re-enable platform decoration (#1542)

Docking: Kept ImGuiDockNodeFlags_PassthruDockspace and removed ImGuiDockNodeFlags_PassthruInEmptyNodes, ImGuiDockNodeFlags_RenderWindowBg. Doesn't include ImGuiDockNodeFlags_NoDockingInCentralNode. (#2109)

Docking: Removed context parameter from internal DockBuilderXXX api at it is expected we transition it to be public facing. (#2109)

Docking: Added ImGuiDockNodeFlags_PassthruDockspace mode (subdivided in three flags: ImGuiDockNodeFlags_NoDockingInCentralNode, ImGuiDockNodeFlags_PassthruInEmptyNodes, ImGuiDockNodeFlags_RenderWindowBg). Added internal facility for register a rectangular hit-test hole in window. Updated DockSpace demo accordingly. (#2109)

Docking: Added ImGuiDockNodeFlags_NoOuterBorder, tweaked DockSpace demo to remove window border. Made docking splitter use the same standard setting as resizing from edges. (#2109)

Docking: Renamed "DocRoot/DocumentRoot" to "CentralNode", more self explanatory. Moved Splitter update higher up in DockNodeUpdate() + minor misc tweak. (#2109)

Docking: Added ImGuiDockNodeFlags_NoDockingInsideDocRootNode flag. Honoring ImGuiDockNodeFlags_NoSplit in child node is already split (so we can use DockBuilder and then lock the layout). Added those options to the demo. (#2109)

Docking: Fixed DockSpace() child window displaying a scrollbar behind the node backgrounds. Rename ImGuiCol_DockingBg to ImGuiCol_DockingEmptyBg. Added ImGuiDockNode::IsLeaftNode(). (#2109)

Merge branch 'viewport' into docking

Merge branch 'master' into viewport ...

# Conflicts:
#	imgui.cpp

Window, Inputs: Fixed resizing from edges when io.MousePos is not pixel-rounded by rounding mouse position input. (#2110)

Window: Resizing from edges (with io.ConfigResizeWindowsFromEdges Beta flag) extends the hit region of root floating windows outside the window, making it easier to resize windows. Resize grips are also extended accordingly so there are no discontinuity when hovering between borders and corners. (#1495, #822, #2110)

Docking: Fixed crash using DockBuilderSplitNode(). (#2109)

Docking: Renamed io.ConfigDockingWithKeyMode to io.ConfigDockingWithShift.

Drag and Drop: Added GetDragDropPayload() to peek directly into the payload (if any) from anywhere. (#143)

Docking: Better tracking of current dock id for inactive and uncreated windows (in settings etc.). + Fixed assert when docking a single-visible leaf node of a hierarchy into another

Docking: Fixes for C++03 compilers.

Docking: Fixed extracting a dock node from a document root: document root should be preserved.

Docking: Reorganizing some of the tab-bar selection and window focus related code.

Docking: Demo: Displaying a message if master docking flag is disabled. + DockSpace() early out + comments.

Docking: Various sanity fixes + fixed tab-bar items sorting issue when docking single window with a dock node into single window without dock node.

Docking: Fix DockContextRebuild() temporarily invalidating dockid reference leading to undesirable merging of nodes.

Docking: Fixed dock node with single window accidental stealing of non-owned host viewport (leading to general havoc).

Style: Added style.TabRounding setting.

Docking: Added DockBuilderCopyDockspace() wip. Added DockBuilderCopyWindowSettings(), renamed DockBuilderForkNode() to DockBuilderCopyNode().

Fixed extraneous static attribute. (#2105)

Fix missing IMGUI_API and mismatching namespace internal's CreateNewWindowSettings (#2105)

Added FindOrCreateWindowSettings() internal helper.

Docking: Reworked DockContextPruneUnusedSettingsNodes() to prune entire unused trees.

Merge branch 'viewport' into docking