Merge branch 'master' into drag_and_drop

Combo: Offset popup position by border size so that a double border isn't so visible. (#707)

Style: Added PopupRounding setting. (#1112)

Fix IsItemHovered() returning true for non-title bar hidden items that are clipped due to window collapsing logic. Fix 27fd1b9. (#823)

Internals: Renamed ImGuiWindow::Accessed to WriteAccessed.

Style: Removed ImGuiCol_ComboBg in favor of combo boxes using ImGuiCol_PopupBg for consistency. (#707)

Internals: Window minor internal renaming + added WindowRounding latch.

Style: renamed style.ChildWindowRounding to style.ChildRounding, ImGuiStyleVar_ChildWindowRounding to ImGuiStyleVar_ChildRounding.

Style: ScaleAllSizes() helper rounds down every values so they are aligned on integers.

Columns: Added ImGuiColumnsFlags_GrowParentContentsSize to internal API to restore old content sizes behavior. (#1444, #125)

Merge branch 'master' into drag_and_drop

Internals: Updating condition/allow flags with a function.

Internals: Window: Store whether the windows has a close button (we need that info for window/tabs dropping preview calculation)

Internals: Added BringWindowToFront(), BringWindowToBack() helpers.

Windows with MenuBar have a larger minimum height to avoid artefacts (I fixed most of the vertical/horizontal artefacts, but the ones in rounded corners were too hard to fix).

Menu: Fixed minor rendering issues on the right size with rounded window when resizing a window small.

Scrollbar: Minor graphical fix for when scrollbar don't have enough visible space to display the full grab.

Minor comments, tweaks

Make it possible to use SetNextWindowPos() on a child window. Useful internally.

Merge branch 'master' into drag_and_drop

Made it guaranteed by API that after calling Begin() the last Item represent the title bar. (#823)

Merge branch 'master' into drag_and_drop

Scrollbar flicker fix for menus/popups (fixes 4d00dd8 and 2df8fa9). Hopefully right this time.

Columns: Clipping columns borders on Y axis on CPU because some GPU drivers appears to be unhappy with triangle spanning large regions (not sure why tbh). (#125) ...

Demo: Columns: Adding a billion of extra lines and using clipper.

Drag and Drop: Added payload->IsPreview() to user can render their custom preview while handling overlapping drop targets. (#143)

Fixed build (3e06450 not meant for master branch, but ok)

Internals: Added ArrowButton() helper.

Drag and Drop: Added internal BeginDragDropTargetCustom() convenient to avoid submitting dummy ItemAdd. (#143)

Fixed scrollbar flickering on/off when uncollapsing a window (fixes 2df8fa9)

io.OptNoCursorBlink -> io.OptCursorBlink (#1427)