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.)

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: Extra clarification for the 100th person who insist on using the OpenGL2 code in spite of existing documentation leaning against it. (#1394)

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()

Examples: GL2: Renaming, comments.

Examples: GL2: rename functions to include GL2 in name

Backup polygon mode, draw with filled polygons, restore state, for clients running opengl with glPolygonMode. closes #798

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: OpenGL2+GLFW/SDL: Added commented out glUseProgram(0) in main.cpp for visibility (#1116)

Examples: SDL2: Tweaked batch files for Win32.

Examples: SDL2: Added build .bat files for win32.