Merge branch 'examples_refactor' into viewport ...

# Conflicts:
#	examples/directx10_example/main.cpp
#	examples/directx11_example/main.cpp
#	examples/directx12_example/main.cpp
#	examples/opengl3_example/main.cpp
#	examples/sdl_opengl2_example/main.cpp
#	examples/sdl_opengl3_example/main.cpp
#	examples/sdl_vulkan_example/main.cpp
#	examples/vulkan_example/main.cpp
#	imgui.h

Examples: Vulkan: SDL: Fixed missing resize handler (not properly merged from #1367) + tweaks.

Examples: Vulkan: Moved code into shared helpers: ImGui_ImplVulkan_SelectSurfaceFormat, ImGui_ImplVulkan_SelectPresentMode.

Examples: Vulkan: Various tweaks to name variable more consistently like Vulkan + a few comments + a few imgui style code compaction.

Viewport: Always be lenient with invalid mouse position during dragging, since they are provided by back-end and technically acceptable inputs + comments. (#1542)

Examples: Vulkan: Debug report tweak + always enable in Debug build.

Examples: Fixed enabling IMGUI_VULKAN_DEBUG_REPORT which was broken during refactor because of duplicate 'extensions' local variable.

Renamed ImGuiNavFlags io.NavFlags to ImGuiConfigFlags io.ConfigFlags. (#787)

Renamed ImGuiNavFlags io.NavFlags to ImGuiConfigFlags io.ConfigFlags. (#787)

Examples: DX10: Multi viewport/platform support (based on DX11 version). (#1542)

Examples: NULL pointers for consistency.

Examples: DX12: Empty skeleton toward implementing the multi-viewport api for DirectX12. (WIP/test API) (#1542, #301)

Examples: SDL: Initial attempt at implementing the viewport/platform api. (WIP/test API) (#1542) ...

ImGui_ImplSDL2_Init() now takes a SDL GL context.

Examples: GLFW + OpenGL3: Initial attempt at implementing the viewport/platform api. (WIP/test API) (#1542)

Examples: DX11 + Win32: Initial attempt at implementing the viewport/platform api. (WIP/test API) (#1542)

Viewport: Initial viewport branch+ platform api commit (squashed from previous commits, still very WIP) (#1542)

Metrics: Added option to show begin order, useful for debugging.

Internal: Minor renaming.

Internals: Moving window: test mouse validity while translating window + using SetWindowPos().

Removed DisplayVisibleMin/DisplayVisibleMax facility (as part of # 1542). Misc comments.

Clearing next window data at the end of Begin() more reliably. Misc comments.

Internals: Settings: Added ReadCloseFn to allow handlers to sanitize data on a per-entry basis.

Examples: Misc tweaks/fixes.

Merge branch 'master' into examples_refactor ...

# Conflicts:
#	examples/opengl3_example/imgui_impl_glfw_gl3.cpp
#	examples/sdl_opengl3_example/imgui_impl_sdl_gl3.cpp

README.md typo fix

ImRect: Removed misleading IsFinite() function used by some Nav code.

Compacted some old Breaking Changes notes (Pre July 2015 stuff)

Changelog: Added all change infos since 1.53 up to the current version.

Changelog: Added Changelog with info from 1.48 to 1.53. Haven't added 1.53..current yet.

TreeNode: Renamed Beta ImGuiTreeNodeFlags_NavCloseFromChild to ImGuiTreeNodeFlags_NavLeftJumpsBackHere. (#1079)