Sisyphus says: tweaked comments about not using old-style OpenGL examples (#1459, #1394 etc.)

Menu bar: better software clipping to handle small windows, in particular child window don't have the minimum constraint added in e9a7e73 so we need to render clipped menus better.

Tweak expression to be less weird (how did that ever happen?)

Update imgui.cpp

Fixed unreferenced variable warnings.

Internals: Added SplitterBehavior(). (#319)

Begin: Fix border size latch when rounding uses Child or Popup value. (#707)

Exposed ImDrawCornerFlags, replaced occurences of ~0 with an explicit ImDrawCornerFlags_All. Inversed BotLeft (prev 1<<3, now 1<<2) and BotRight (prev 1<<2, now 1<<3).

Color picker: Tweak vertex shading code, since we aren't shading between PrimReserve and PrimVert the code can be expressed more naturally. (#346)

Style, Begin: removed ImGuiWindowFlags_ShowBorders window flag. Borders are now fully set up in the ImGuiStyle structure (see e.g. style.FrameBorderSize, style.WindowBorderSize). Use ImGui::ShowStyleEditor() to look them up. (#707, fix #819, #1031, ref #1019, ref #447)

Reorder fields for consistency.

Style: renamed ImGuiCol_ChildWindowBg to ImGuiCol_ChildBg. (#707)

NewFrame() now asserts if neither Render or EndFrame have been called. Exposed EndFrame(). Made it legal to call EndFrame() more than one. (#1423 etc.)

NewFrame(): using literal strings in the most-frequently firing IM_ASSERT expression to increase the odd of programmers seeing them (especially those who don't use a debugger).

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)

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