Merge branch 'master' into viewport ...

# Conflicts:
#	examples/sdl_opengl2_example/main.cpp
#	examples/sdl_opengl3_example/main.cpp
#	examples/vulkan_example/main.cpp

ImVector: Fixed insert() helper using the = operator (followup to be consistent with 4186c2c)

Viewport, Platform: Added void* to render/swap buffer functions. Comments. (#1542, #1042)

Nav: Track nav input source more generally (gamepad vs keyboard) (#787) + update todos and demo tweaks

Viewport, Platform: Refactored platform interface. Removed need to use imgui_internal.h in backends. Split viewport into public facing ImGuiViewport and internal structure. Exposing enough data to provide custom tweaked renderers. Renamed handlers, fixed lots of inconsistencies. (#1542, #1042)

Merge branch 'master' into viewport ...

# Conflicts:
#	imgui.h

imgui.h: Various comments and tweaks.

imgui.h: Moved columns lower in the file. Various spacing changes and minor comments.

Merge branch 'master' into viewport ...

# Conflicts:
#	imgui.h

ImVector: Added copy/assign operators as helpers to ease cloning of data.

ImDrawList: Added Clone() helper function.

ImVector: resize() / push_back() use memcpy() as we are not supposed to be constructor/destructor/operator aware at all. (If we do need to rework ImVector). In turn this will allow us to define assign/copy operators.

ImVector: Using value_type consistently. Spacing.

Update TODO list, minor fix in Readme, comments, Clang -Weverything warning fix in imgui_draw.cpp under Windows.

Examples: SDL,GLFW,Vulkan: The Platform<>Renderer link is handled by SDL/GLFW platforms, both can compile without Vulkan headers, SDL+Vulkan is now on part with GLFW+Vulkan (aka broken the same way!). (#1542)

Viewport: Fixed software mouse cursor from appearing in all multiple lists simultaneously. (#1542)

Viewport: Obsoleted io.DisplayPos (which was a Viewport branch thing), added ImDrawData::DisplayPos, DisplaySize (#1542) wip

Merge branch 'master' into viewport

Moved IM_NEW, IM_DELETE helpers to imgui.h for convenient use by back-ends and user code.

ImVector: Spacing, assert tweaks

Misc: Fix 111ea7a, GetStyleColorName() would assert, removed removed ImGuiCol defines (too much risk/complexity trying to silently ignore it).

Examples, Viewport: Vulkan: Experiment (broken) multi-viewport support, merging code from ParticlePeter branches. (#1542, #1042)

Merge branch 'master' into viewport (inc Vulkan resize fix merge #1042)

Misc comments, todos + reintroduced removed ImGuiCol defines under !IMGUI_DISABLE_OBSOLETE_FUNCTIONS wrap.

Style: CloseButton() now display a proper cross. Using Button colors for background. Removed ImGuiCol_CloseButton, ImGuiCol_CloseButtonActive, ImGuiCol_CloseButtonHovered as the closing cross uses regular button colors now. (#707)

Viewport, DPI: Some early work on per-viewport DPI support. At the moment the easiest way is to replace fonts during the ChangedViewport callback, but down the line we should aim at handling some of it at ImFont level. (#1542, #1676)

ImFont: Added FindGlyphNoFallback. Fixed MergeMode broken by 1ef1acb

Merge branch 'master' into viewport

Viewport,Platform: Added GetWindowDpiScale() platform interface, changes of scale are reflected by positioning and resizing windows in their given viewport. (#1542)

Viewport: Changed signature of ResizeViewport to be consistent with other similar functions.