Merge branch 'context' ...

# Conflicts:
#	examples/allegro5_example/main.cpp
#	examples/directx10_example/main.cpp
#	examples/directx11_example/main.cpp
#	examples/directx9_example/main.cpp
#	examples/marmalade_example/main.cpp
#	examples/opengl2_example/main.cpp
#	examples/opengl3_example/main.cpp
#	examples/sdl_opengl2_example/main.cpp
#	examples/sdl_opengl3_example/main.cpp
#	examples/vulkan_example/main.cpp

Nav: Examples: Added commented out io.NavFlags |= ImGuiNavFlags_EnableKeyboard to all examples. (#787)

Added ImGuiKey_Space, mapped in every examples. Will be required for navigation. (#787)

Merge branch 'master' into context

Merge branch 'master' into navigation

Examples: SDL: Using SDL_GetPerformanceCounter() / SDL_GetPerformanceFrequency() to handle framerate over 1000 fps properly. Noticed bad inputs artefacts in Nav branch at 2000 fps without this. (#996)

Examples: SDL2: Enabling vsync. Using scancode consistently, fixed keyboard weirdness.

Examples: Organized header files to make available features more visible.

Merge branch 'master' into context

Moved extra_fonts/ to misc/fonts/. Moved .natvis file to misc/natvis/ (#1569)

Examples: Using Dark theme by default. (#707). Tweaked demo code.

Examples: Using #include "imgui.h" instead of <imgui.h> appear correct-er as per standard? xcode+clang are very nitpicky there.

Fix sdl_opengl2_example filename in README.md's build instructions

Examples: Updated for reorganized context functions. Calling CreateContext(), DestroyContext() in example code. Removed Shutdown() from binding code. (#1565, #586, #992, #1007, #1558)

Examples: Simplified mouse wheel handling. (#1463)

Horizontal mouse wheel: renamed io.MouseHorizWheel to io.MouseWheelH. Reorganized the code in NewFrame(). Examples: Updated GLFW+GL and SDL+GL accordingly. (#1463)

Merge branch 'tseeker/20171127-feature-horiz-wheel' of https://github.com/tseeker/imgui into tseeker-tseeker/20171127-feature-horiz-wheel ...

# Conflicts:
#	examples/sdl_opengl2_example/imgui_impl_sdl_gl2.cpp
#	examples/sdl_opengl3_example/imgui_impl_sdl_gl3.cpp

Examples: SDL: Using SDL_CaptureMouse() to retrieve coordinates outside of client area when dragging. (#1559) ...

Digging into sdl window/mouse stuff will also be useful for multi-viewport work.

Examples: SDL: Minor renaming.

Examples: SDL+GL2: Renamed imgui_impl_sdl.* to imgui_impl_sdl_gl2.* for consistency and to emphasis on GL2-ness.

Examples: SDL: Minor renaming.

Examples: SDL: Using SDL_WINDOW_INPUT_FOCUS instead of SDL_WINDOW_MOUSE_FOCUS (which is ~~hovered). We should use SDL_CaptureMouse + SDL_WINDOW_MOUSE_CAPTURE_FLAG which requires SDL 2.0.4 will give it a try shortly. (#1559)

Examples: SDL: Fixed mapping of Insert key (#1555, fix bug introduced in #1541)

Added ImGuiKey_Insert for future use. Setup in all example bindings. (#1541)

Examples: Using IM_OFFSETOF macro. + Comments

Examples: Comments about invalid mouse pos.

Examples: Comments, synched some minor drift between examples + stronger suggestion to use StyleColorsDark().

Renamed the emblematic ShowTestWindow() function to ShowDemoWindow(). Kept redirection function (will obsolete).

Horizontal mouse wheel support ...

This patch adds support for the horizontal mouse wheel in ImGui. It
affects windows that can be scrolled, as long as the Ctrl key is not
being pressed.

The scrolling speed has been set empirically so that it matches the
scrolling speed on the Firefox browser when the horizontal wheel is
used.

Internally, it adds a MouseHorizWheel to ImGuiIO, which is then used in
NewFrame to scroll the current window.

The SDL/GL2, SDL/GL3, GLFW/GL2 and GLFW/GL3 examples has been modified
to use it.

Sisyphus says: tweaked comments about not using old-style OpenGL examples (#1459, #1394 etc.)