Examples: Vulkan: Fix (something changed in GLFW not including vulkan.h, was unwillingly relying on that)

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)

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.

Examples: Vulkan: FIxed warnings in 32-bit modes (vulkan uses VkDeviceSize which is always 64-bit long)

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)

Examples: Allegro, Apple, DirectX9/10/11, Glfw+Vulkan :Added support for horizontal mouse wheel. (#1463)

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

Examples: Comments about invalid mouse pos.

Examples: Vulkan: Tweak

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).

Examples: Added a bunch of comments/referencs related to io.WantCaptureMouse, io.WantCaptureKeyboard (#1262, #1237, #1219, #635, #1058, #1051, #912, #533, #703, #446, #459, #364, #213, #52, and more)

Examples: Added more comments near the fonts loading section, to catch common questions and errors (e.g. #1397, #1366, #1341, #1222, #1193, #1115, #951, etc.)

Examples: Adding Roboto to the commented-out font list, and removing the unnecessary ProggyClean from there.

Examples: Avoid using ImColor() to not tempt newcomers into looking at it

Examples: Main: Removed call to SetNextWindowSize()

IO: io.MousePos needs to be set to ImVec2(-FLT_MAX,-FLT_MAX) when mouse is unavailable/missing. Previously ImVec2(-1,-1) was enough but we'll now accept negative mouse coordinates.

Renamed ImGuiSetCond_XXX type and enums to ImGuiCond_XXX, kept old enums under #ifdef IMGUI_DISABLE_OBSOLETE_FUNCTIONS

Examples: Vulkan: Batch file builds both debug and release

Examples: Vulkan: Fixed an extra validation (tested on Windows with VulkanSDK 1.0.46.0) (#1042)

Examples: Vulkan: Various very minor stylistic fixes, fixing typos in comments, etc. (#1042 #1043)

Image presentation now depends on the completeness of command buffer submission through semaphores. ...

To maintain maximum frame rate we render to the last acquired swapchain image but present the last but one drawn image. This behavior is optional through conditional compilation macros.

Removed redundant VkResult plugged into VkPresentInfoKHR pResults attribute. This is only meaningful when we present directly to multiple swapchains. In that case we can an VkResult per swapchain.