Merge branch 'viewport' into docking ...

# Conflicts:
#	examples/example_allegro5/main.cpp
#	examples/example_marmalade/main.cpp

Merge branch 'master' into viewport + comments ...

# Conflicts:
#	examples/imgui_impl_opengl3.cpp
#	imgui.cpp

Nav: Fixed an assert in certain circumstance (mostly when using popups) when mouse positions stop being valid. (#2168) + adding a else block to make NavCalcPreferredRefPos() more explicit.

Viewport: BeginMainMenuBar(): explicitly set viewport to avoid creating new one when ImGuiConfigFlags_ViewportsNoMerge is set + misc shallow changes.

Viewport: BeginMainMenuBar(): explicitly set viewport to avoid creating new one when ImGuiConfigFlags_ViewportsNoMerge is set + misc shallow changes.

Docking: Fixed a regression where clicking a Tab wouldn't immediately set NavWindow. Which led to breaking the NavSaveLastChildNavWindow/NavRestoreLastChildNavWindow logic. (#2109)

Examples: OpenGL3: Added support for GL 4.5's glClipControl(GL_UPPER_LEFT). (#2186)

Made IsWindowFocused() work outside of NewFrame()-EndFrame() and added comments about how ImGuiFocusedFlags_AnyWindow should NOT be used in place of io.WantCaptureMouse. (#2185)

Update README.md

Internals: DragBehavior: Added support for ImGuiDragFlags_Vertical to implement a vertical drag widget (no frontend function provided).

Internals: SliderBehavior: Using axis indexing.

Merge branch 'master' into viewport + specific changes for GLFW callbacks ...

# Conflicts:
#	examples/example_glfw_opengl3/main.cpp
#	examples/example_win32_directx11/main.cpp
#	examples/example_win32_directx9/main.cpp
#	examples/imgui_impl_glfw.cpp

Examples: GLFW: User previously installed GLFW callbacks are now saved and chain-called by the default callbacks. (#1759)

Examples: Misc comments mainly related to GLFW callbacks. (#1759)

Examples: OpenGL3+GLFW/SDL: Made main.cpp compile with IMGUI_IMPL_OPENGL_LOADER_CUSTOM (may be missing init). (#2178)

Merge branch 'viewport' into docking

Examples: SDL: Tweaked Windows instructions and batch files. (#2175)

Viewport: Fixed SDL+OpenGL2 example to work with multi-viewports. (#2175)

Examples: SDL: Tweaked Windows instructions and batch files. (#2175)

Examples: Win32: Handle UTf-8 in platform window title setting. (#2164)

Merge branch 'master' into viewport

Examples: GLFW: VS2015 project link with legacy_stdio_definitions.lib in order to link with the precompiled VS2010 GLFW3.lib we provide. (#2010, #2043, #2091)

Config: Added IMGUI_DISABLE_WIN32_FUNCTIONS to disable linking with _any_ Win32 function, as a general forward compatible measure.

ListBox(): Fixed frame sizing when items_count==1 unnecessarily showing a scrollbar. (#2173). Tweaked frame sizing so list boxes will look more consistent when FramePadding is far from ItemSpacing.

Doc: Fixed comments referring to LoadFromFileTTF() instead of AddFontFromFileTTF() (#2153)

Examples: Add missing include guards (#2166)

Examples: Vulkan: Avoid unreferenced parameter warning. (#2162)

Internals: Moved the FocusableItemUnregister() outside of InputScalarAsWidgetReplacement(), it should not be here and doesn't facilitate reusing InputScalarAsWidgetReplacement(). (cc #2155)

gladLoadGL() return 0 to indicate failure (#2157)

Merge branch 'viewport' into docking ...

# Conflicts:
#	imgui_demo.cpp