Simplified return of ImGui::IsKeyReleased()

ImFontAtlas: Moved mouse cursor data out of ImGuiContext, fix drawing them with multiple context. Also remove the last remaining undesirable dependency on GImGui in imgui_draw.cpp, finishing the work recently done with ImDrawListSharedData. Hurra! (#939)

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

Renaming for consistency.

Basic undocumented/unsupported combination of Child+Tooltip. The full feature needs substancially more work but this is enough for simplest cases. (#1345)

Begin: Removed asserts that got in the way of some flags combination. (#1345)

MovingWindow: Track click offset based on root window (undo 514d30d). This should not affect the patch used for #1345 as the RootWindow for Child+Tooltip window points to itself now.

DragFloat: Fix/workaround for backends which do not preserve a valid mouse position when dragged out of bounds. (#1559)

Drag and Drop: Increased payload type string to 12 characters instead of 8.(#143)

NewFrame(): Added an assert to detect incorrect filling of the io.KeyMap[] array earlier. (#1555) + comments.

InputText: Cursor X position not lost when clicking outside on an item that's submitted after the InputText(). It was only noticeable when restoring focus programmatically. (#1418, #1554)

Internal: DrawData: Tidying, renaming.

Internals: DrawData: We don't need an intermediate layer for popups.

Metrics: Tweaks to hover-window-drawlist to see window bounding box.

Internals: DrawData: Refactored chunks into a ImDrawDataBuilder we can reuse.

Internals: DrawData: renamed fields only (committing separately so that next commit is less nosiy).

MovingWindow: Track click offset based on MovingWindow and not its RootWindow. Followup to 3849bb4. Comments + adding a local to ease patch #1345.

Fix cross compilers

Internals: Merge of harmless stuff from Navigation stuff. Added GetHoveredID() internal helper.

Begin: FIx previous commit - no need to call on collapsed window. Handle manual resize (grip, border, gamepad) before setting up window DrawList main clipping rectangle. Sane (and required for viewport code). (#822, #1542)

Begin: Handle manual resize (grip, border, gamepad) before setting up window DrawList main clipping rectangle. Sane (and required for viewport code). (#822, #1542)

MovingWindow: Proper fix for 651538e attempt, without altering MovingWindow which has side-effects. Clicking on a window with the ImGuiWIndowFlags_NoMove flags takes an ActiveId so we can't hover something else. (ref #1381, #1337)

Revert "Clicking on a window with the ImGuiWIndowFlags_NoMove flags takes an ActiveId so we can't hover something else. (ref #1381, #1337)" ...

This reverts commit 651538e.

Begin: Shuffling bits of code around.

Clicking on a window with the ImGuiWIndowFlags_NoMove flags takes an ActiveId so we can't hover something else. (ref #1381, #1337)

Added ImGuiHoveredFlags_AnyWindow, ImGuiFocusedFlags_AnyWindow. Obsoleted IsAnyWindowHovered()/IsAnyWindowFocused() in favor of IsWindowHovered(ImGuiHoveredFlags_AnyWindow)/IsWindowFocused(ImGuiFocusedFlags_AnyWindow). Added to demo. (#1382)

Internals: Begin: Refactor some code into an UpdateManualResize() function.

Internals: Begin: Moved DrawList setup code below, the viewport system will need to push the outer clipping rectangle as late as possible.

Begin: Moving some code around for the benefits of the wip viewport branch.