Merge branch 'master' into viewport ...

# Conflicts:
#	examples/opengl2_example/imgui_impl_glfw_gl2.cpp
#	examples/opengl3_example/imgui_impl_glfw_gl3.cpp
#	examples/sdl_opengl3_example/imgui_impl_sdl_gl3.cpp
#	examples/sdl_opengl3_example/imgui_impl_sdl_gl3.h
#	examples/vulkan_example/imgui_impl_glfw_vulkan.cpp

Drag and Drop: Source doesn't report as hovered (at a lower-level). Source disable AllowOverlap flag if any set. (#143)

Drag and Drop: BeginDragDropSource(): Offset tooltip position so it is off the mouse cursor, but also closer to it than regular tooltips, and not clamped by viewport. (#1739)

BeginCombo(), BeginMainMenuBar(), BeginChildFrame(): restore modified style at end of Begin instead of End so doesn't affect child windows, BeginTooltip() etc.. (allowed since 7b6b703)

Added float GetWindowDpiScale(). (#1542, #1676)

Viewport, Platform: Fixed a crash if the back-end set the PlatformRequestMove/PlatformRequestSize flags while viewports were disabled (it happened in the SDL back-end, and generally we want to tolerate it to make back-end implementation simpler). (#1542)

ColorEdit3, ColorEdit4, ColorButton: Added ImGuiColorEditFlags_NoDragDrop flag to disable ColorEditX as drag target and ColorButton as drag source. (#1826)

Viewport: Fixed using ImGuiConfigFlags_ViewportsNoMerge always showing the Debug window by testing the Active flag as well. (#1542)

Fixed GCC pre-8 build. (#1822) + added bonus the non-ASCII character pasted from GCC breaks my SourceTree/Git combo

Merge branch 'master' into viewport ...

# Conflicts:
#	examples/opengl3_example/imgui_impl_glfw_gl3.cpp
#	examples/sdl_opengl3_example/imgui_impl_sdl_gl3.cpp
#	imgui.cpp
#	imgui.h

Disabled GCC 8.1.0 warnings -Wclass-memaccess (#1822)

Remove trailing white spaces.

Internals: Forward declaring and commenting internal structures. Renamed ImGuiDrawContext to ImGuiWindowTempData, but kept .DC member name for backward compatibility purpose

Viewport: Made GetWindowViewport() not flag the window as written to.

Comments + Internals: Selectable: decoupled internal flags and removed their menu / menu-item semantic as upcoming changes are requiring more flexibility.

Viewport: When resizing/moving a window using the host OS/WM we attempt to merge back into host viewport. (#1542)

Viewport: Added GetWindowViewport() to query the current viewport for the current window. Comments. (#1542)

TreeNode: Fixed nodes with ImGuiTreeNodeFlags_Leaf flag always returning true which was meaningless. Tweak demo.

Nav: Draft internal api to forward move request with loop/wrap options. Will rework for parallel scoring of two paths (as a generalization of the NavFlattened concept). (#787)

Nav: To keep the navigated item in view we also attempt to scroll the parent window as well as the current window. (#787)

Version 1.62 WIP

Merge branch 'master' into viewport ...

# Conflicts:
#	imgui.cpp

Version 1.61 + todo additions

ColorEdit: Fixed not being able to pass the ImGuiColorEditFlags_NoAlpha or ImGuiColorEditFlags_HDR flags to SetColorEditOptions(). Demo tweak.

Fix for atof with glibc.

Added ImAtof, ImCeil, ImFloorStd to IMGUI_DISABLE_MATH_FUNCTIONS for consistency. Configuration comments.

Added IMGUI_DISABLE_MATH_FUNCTIONS in imconfig.h to make it slightly easier to redefine wrappers to std maths functions such as fabsf(), fmodf(), etc. Comments.

Data types: DragScalar: Fixed speed of integer values tweaking with keyboard/gamepad when speed < 1. Enforce min/max bounds when power curves are used. SliderScalar: Fixed integer/slow tweaking. (#643)

Merge branch 'master' into viewport ...

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

Data types: DragScalar, InputScalar: default parameters. Added IM_STATIC_ASSERT(). Comments.