Merge branch 'master' into navigation

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

Examples: Makefile leave CXX alone, instead leave commented out options. (nb: codeship doesn't seem have clang++)

Examples: Use Clang in old Makefile.

Examples: Synced Makefile comments. Added build/ folder into git ignore list/

Nav: Examples: Glfw+GL3: Added basic gamepad mapping code when io.NavFlags & ImGuiNavFlags_EnableGamepad is set. (will iterate/tweak before spreading to other examples). (#787)

Nav: Examples: DirectX11, Glfw+GL3: Basic code to map keyboard inputs when io.NavFlags & ImGuiNavFlags_EnableKeyboard is set. (will iterate/tweak before spreading to other examples). (#787)

Merge branch 'master' into context

Added imgui.natvis helper for visual studio users. Added to examples projects.

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

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

Examples: OpenGL3+GLFW: Using 3.2 context + GLSL version 150 (#1466)

Examples: Using IM_OFFSETOF macro. + Comments

Examples: Visual Studio projects: Disabled extraneous function-level check in Release build.

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.

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: Comments to guide people unfamiliar with the librairies used.

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: GLFW+GL2/GL3: Minor tweaks, comments.

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

Nav/Examples: honoring the io.WantMoveMouse flag in most common examples (#323) ...

Missing support Vulkan (#549), Apple (#575, #247), SDL (#58, #356),
Allegro, Marmalade (#368, #375)

Examples: Main: Removed call to SetNextWindowSize()

Examples: GL3: Comments, tweaks (#1145)