Improved algorithm for mitre joints on thick lines

Popups: Closes popup at the time of FocusWindow(). Fixes right-click from closing all popups instead of aiming at the hovered popup level (regression in 1.67's ae76a1fd).

Misc comments, internal renaming, added disable indentation option to Columns demo section.

Added SetNextItemWidth() helper to avoid using PushItemWidth/PopItemWidth() for single items.

Demo: Documents: Fix misusage of ListBoxHeader().

Internals: Columns: Tweaks, renaming. Metrics: Show rectangles for child windows. ...

Renamed SameLine() first parameter.

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, Docs: Added a bunch of clarification about ButtonBehavior in the form of a table (and to facilitate writing tests)

Demo: Comments, tweaks, removed some uses of ImColor helpers.

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

Not using isprint. + todo items.

Examples: Vulkan: Added missing support for 32-bit indices (#define ImDrawIdx unsigned int). + demo typo

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)

Examples: OpenGL: Added a dummy GL call + comments in ImGui_ImplOpenGL3_Init() to detect uninitialized GL function loaders early, and help users understand what they are missing. (#2421)

Version 1.70 WIP

Demo: Custom rendering: Minor sizing issue fix.

Version 1.69, comments, typos

Fixed Clang and PVS warnings.

Demo: InputText: Demonstrating use of ImGuiInputTextFlags_CallbackResize. (#2006, #1443, #1008).

Added ImGuiColorEditFlagsFlags_InputHSV. (#2383, #2384)

Demo: Renamed ShowHelpMarker() -> HelpMarker(). Fixed minor PVS warning. Removed unnecessary casts.

InputTextWithHint: Fix for Password fields. Update changelog, demo. (#2400)

Added InputTextWithHint() (#2400) ...

Squashed commit of the following:

commit 1970d84
Author: Lucas Lazare <lazarelucas@yahoo.fr>
Date:   Tue Mar 5 12:20:39 2019 -0500

    Removing sneaky tabulations #2 (why, editor T-T)

    I should update my settings, I guess

commit 219bdfc
Author: Lucas Lazare <lazarelucas@yahoo.fr>
Date:   Tue Mar 5 12:17:27 2019 -0500

    Removing useless check introduced in b0d172

commit 8afd7a2
Author: Lucas Lazare <lazarelucas@yahoo.fr>
Date:   Tue Mar 5 11:49:24 2019 -0500

    Removing sneaky tabulations

commit 8e04908
Author: Lucas Lazare <lazarelucas@yahoo.fr>
Date:   Tue Mar 5 11:45:13 2019 -0500

    Moving InputTextHinted code to InputTextEx

commit b0d1723
Author: Lucas Lazare <lazarelucas@yahoo.fr>
Date:   Tue Mar 5 00:23:02 2019 -0500

    C++11 to C++98

commit 9afeae3
Author: Lucas Lazare <lazarelucas@yahoo.fr>
Date:   Mon Mar 4 23:43:28 2019 -0500

    Added InputTextHinted

Demo: Added flags to InputTextMulttiline() demo.

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

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

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.

DragScalar, InputScalar, SliderScalar: Added support for u8/s8/u16/s16 data types. We are reusing function instances for larger types to reduce code size. (#643, #320, #708, #1011)

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]

add _Show prefix to color flags that control inputs, rename __InputsMask to __ShowMask ...

This is anticipation of changing __InputsMask to control the format of
input colors, and adding _InputRGB and _InputHSV to change how input
colors are interpreted.