Merged a bunch of small changes from Docking branch to reduce the difference between branches. ...

Noticeable: horizontal alignment of CloseButton. Menu fill take account of border. Various stylistic tweaks to accomodate other changes in Docking.

Internals: Columns: Some renaming, extracted code into GetColumnsID().

Internals: Moved resize grips and borders to nav layer 1 so that testing system doesn't attempt to scroll to get them inside the InnerRect.

Tests: Added hook/tweaks for imgui-test engine. + Fixed warnings.

Internals: Merge minor things from range_select branch. Added ImGuiButtonFlags_NoHoveredOnNav. Added IsItemToggledSelected() - unused here. Renaming.

FAQ tweaks. Add missing entries in imgui.cpp (which until now where only in the README).

Misc: Added IM_MALLOC/IM_FREE macros mimicking IM_NEW/IM_DELETE so user doesn't need to revert to using the ImGui::MemAlloc()/MemFree() calls directly.

Tabs to Spaces, comments.

InputText: Work-around for buggy standard libraries where isprint('\t') returns true. (#2467, #1336) ...

Not using isprint. + todo items.

Internals: Renamed the ImGuiWindow HiddenFrameXXX fields to decorrelate them from resizing behavior, as those values are set by other logic.

Rearrange code in UpdateMouseWheel(). (#2424, #1463) + Fix old io.FontAllowUserScaling feature (probably should be made obsolete, but until then best fixed)

Implement horizontal scrolling with Shift+Scroll ...

This is standard scrolling behaviour in most applications.

IsWindowHovered() made change which should have no effect in master but fix result of IsWindowHovered(ImGuiHoveredFlags_ChildWindows) over multiple viewport in docking branch. (#2432)

Comments, todo list, remove trailing spaces.

GetMouseDragDelta(): also returns the delta on the mouse button released frame. Verify that mouse positions are valid otherwise returns zero. Removed obsolete comment. Tweaked demo. (#2419)

Version 1.70 WIP

Version 1.69, comments, typos

Internals: Fixed Navigation from reaching ImGuiItemFlags_Disabled items (#211) + Examples comments

Fix typos. (#2413)

Don't use const qualified parameters in declarations. ...

This fixes warnings from clang-tidy like this:

    parameter 'v_max' is const-qualified in the function declaration;
    const-qualification of parameters only has an effect in function definitions

Since values (rather than references or pointers) don't need to be
const, they don't need to be marked that way in the function declaration.

Moved placeholder sections to match Docking branch. Comments.

Internal: Columns: Allow to use BeginColumns(1) so code designed for variable number of columns can still call NextColumn etc. (#125)

Fixed IsItemDeactivated()/IsItemDeactivatedAfterEdit() from not correctly returning true when tabbing out of a focusable widget (Input/Slider/Drag) in most situations. (#2215, #1875) ...

+ Minor renaming of a local variable in widget code.

Internal: Tabbing/Focus: Tidying up old code, moved some state to context instead of window. Storing new data will allow us to fix the bug mentioned in #2215 (probably in next commit).

Internal: Tabbing: Tweaks to FocusableItemRegister and using the standard mechanism to allow/block Tab being interpreting by tabbing instead of InputText() widget.

Nav: Fixed Ctrl+Tab keeping active InputText() of a previous window active after the switch. (#2380)

Renamed GetOverlayDrawList() to GetForegroundDrawList() for consistency. Kept redirection function (will obsolete). (#2391) ...

Demo: Using GetBackgroundDrawList() and GetForegroundDrawList() in "Custom Rendering" demo.

Added GetBackgroundDrawList() helper to quickly get access to a ImDrawList that will be rendered behind every other windows. (#2391)

Misc: Asserting in NewFrame() if style.WindowMinSize is zero or smaller than (1.0f,1.0f). Internal: ImHash functions tweaks. Added InputText() to query status section.

Renamed ColorEdit/ColorPicker's ImGuiColorEditFlags_RGB/_HSV/_HEX flags to respectively ImGuiColorEditFlags_DisplayRGB/_DisplayHSV/_DisplayHex. This is anticipation of adding new flags to ColorEdit/ColorPicker functions which would make those ambiguous. (#2384) [@haldean]