Fixed unused variables warnings when asserts are compiled out. (#2551)

Platform Binding for GLFW updated with the release of GLFW 3.3 (#2547) ...

* With the release of GLFW 3.3, it is now possible to detect correctly monitors working area (see GLFW_HAS_MONITOR_WORK_AREA). GLFW 3.3 also introduced the window hint GLFW_FOCUS_ON_SHOW. This fixed the case where a new created window (viewport) takes the focus even if not visible.

* Disable a GLFW 3.2 windows hack when GLFW 3.3 is detected (related to window focused when shown).

Fixed a PVS Studio static analyzer warning.

Merge branch 'master' into docking ...

# Conflicts:
#	docs/CHANGELOG.txt
#	imgui.cpp

Internal: Extracted some of the Begin code into RenderWindowDecorations().

Internal: Extracted some of the Begin code into RenderWindowTitleBarContents().

Internal: Begin: Update rectangles before Scrollbar() which now uses them. Fixes 39eeda0.

Internal: Scrollbar: Further sane simplification (using InnerMainRect instead of duplicating calculations).

Internal: Scrollbar: Extracted scrollbar code for other uses (eg. table v2 scrolling without using a child window).

Separator: Revert 1.70 "Declare its thickness (1.0f) to the layout" change (c5d83d8a). It's not incorrect but it breaks existing some layout patterns. Will return back to it when we expose Separator flags.

Internals: Columns: Renamed fields. Comments and tweak. Moved a demo block.

Internal: Refactored Separator into SeparatorEx(), exposed ImGuiSeparatorFlags_SpanAllColumns in imgui_internal.h and support without. (#759) + misc comments

Columns: Fixed Separator from creating an extraneous draw command. Fixed Selectable with SpanAllColumns flag from creating an extraneous draw command. (#125)

Viewports: Minor tweaks. (#2471)

Viewports: Fix to avoid SetNextWindowViewport being overrided by creation of a standalone viewport. (#2544, #1542)

Version 1.71 WIP + fixed minor typo

Version 1.70

Examples: DirectX9: Fixes for multi-viewports. Avoid using a depth/stencil target for secondary viewport. (#2520, #2502)

Examples: DirectX9: Fixes for multi-viewports, destroying all swap chains. (#2520, #2502)

Merge branch 'master' into docking ...

# Conflicts:
#	examples/README.txt
#	examples/imgui_impl_dx9.cpp
#	imgui.cpp
#	imgui.h

Examples: DirectX9/10/11: Taking reference to device + subsequent merge of this in docking will fix DX9 issue #2524

Examples Readme and Changelog tweaks, added #2527, re-ordered examples/README alphabetically.

Examples: Metal: Add GLFW+Metal example

Removed git merge leftovers

Window: Fixed SetNextWindowSizeConstraints() with non-rounded positions making windows drift. (#2067, #2530)

Misc: Made IMGUI_CHECKVERSION() macro also check for matching size of ImDrawIdx.

Internals: Fixed incorrect repeat delay/rate calculation in IsMouseClicked() with repeat flag leading to involontary but thankfully doubling the rate. Using our standard function, making the multiplicator explicit.

Selectable: With ImGuiSelectableFlags_AllowDoubleClick doesn't return true on the mouse button releas efollowing the double-click. Only first mouse release + second mouse down (double-click) returns true. Likewise for internal ButtonBehavior() with both _PressedOnClickRelease | _PressedOnDoubleClick. (#2503)

Demo: Improved trees in columns demo. (#2136)

Internals: Rename GetContentRegionMaxScreen() -> GetWorkRectMax(). At this point this is mostly useful to facilitate merge of other branches.