Merge branch 'master' into docking

Examples: Metal: Compilation fix.

Examples: OpenGL2: Added #define GL_SILENCE_DEPRECATION to cope with newer XCode warnings.

Viewport: SDL: Inherit SDL_WINDOW_ALLOW_HIGHDPI flag from main viewport. (#2306)

Merge branch 'master' into docking ...

# Conflicts:
#	examples/imgui_impl_opengl2.cpp
#	examples/imgui_impl_opengl3.cpp
#	imgui.cpp
#	imgui_widgets.cpp

Examples: SDL: Using the SDL_WINDOW_ALLOW_HIGHDPI flag. (#2306, #1676) [@rasky]

ImDrawData: Added FramebufferScale field (currently a copy of the value from io.DisplayFramebufferScale). ...

This is to allow render functions being written without pulling any data from ImGuiIO, allowing incoming multi-viewport feature to behave on Retina display and with multiple displays. If you are not using a custom binding, please update your render function code ahead of time, and use draw_data->FramebufferScale instead of io.DisplayFramebufferScale. (#2306, #1676)
Examples: Metal, OpenGL2, OpenGL3: Fixed offsetting of clipping rectangle with ImDrawData::DisplayPos != (0,0) when the display frame-buffer scale scale is not (1,1). While this doesn't make a difference when using master branch, this is effectively fixing support for multi-viewport with Mac Retina Displays on those examples. (#2306) Also using ImDrawData::FramebufferScale instead of io.DisplayFramebufferScale.
Examples: Clarified the use the ImDrawData::DisplayPos to offset clipping rectangles.

Examples: Metal: Removed unnecessary loop. Fixed OSX Clang warning in imstb_truetype. (#1929, #1873)

Merge branch 'master' into docking ...

# Conflicts:
#	imgui.cpp
#	imgui_demo.cpp

Minor tweaks to reduce false positive of PVS Studio static analyzer.

Examples: SDL: Fix for Emscripten/Android/iOS on Docking branch.

Merge branch 'master' into docking ...

# Conflicts:
#	examples/imgui_impl_opengl3.cpp
#	imgui.cpp
#	imgui.h

Examples: Made imgui_impl_win32 drag gdi32.lib for GetDeviceCaps(). (#2327)

Examples: OpenGL3: Using GLSL 4.10 shaders for any GLSL version over 410 (e.g. 430, 450). (#2329) [@BrutPitt]

Viewport: Added ImGuiViewportFlags_NoFocusOnClick + support in imgui_impl_win32. Made windows with no decoration always set the _NoFocus flags. (#1542, #2117) ...

Fix e.g. clicking on protruding combo box stealing highlight from parent window with decoration.

Merge branch 'master' into docking ...

# Conflicts:
#	imgui.cpp

Examples: DirectX9: Fix Clang warning.

Merge branch 'viewport' into docking ...

# Conflicts:
#	imgui.cpp
#	imgui_internal.h

Merge branch 'master' into viewport ...

# Conflicts:
#	examples/README.txt
#	imgui.cpp

Removed trailing spaces from text files. (#2038, #2299)

Merge branch 'viewport' into docking ...

# Conflicts:
#	docs/CHANGELOG.txt
#	imgui.cpp
#	imgui_draw.cpp

Merge branch 'master' into viewport ...

# Conflicts:
#	examples/example_sdl_vulkan/main.cpp
#	examples/imgui_impl_dx11.cpp
#	examples/imgui_impl_dx12.cpp
#	examples/imgui_impl_glfw.cpp
#	examples/imgui_impl_sdl.cpp
#	examples/imgui_impl_vulkan.h
#	imgui.cpp

Examples: OpenGL2: Added (yet another) comment/instruction against using opengl2 with modern OpenGL. (#2297)

Removed trailing spaces (#2038, #2299)

Merge branch 'master' into viewport ...

# Conflicts:
#	examples/imgui_impl_win32.cpp

Examples: Win32: Using wc.lpszClassName instead of duplicating the literal. + tweak README format.

Examples: Win32: Added support for mouse buttons 4 and 5 via WM_XBUTTON* messages. (#2264)

Examples: Win32: Fix for older Windows SDK.

Merge branch 'viewport' into docking ...

# Conflicts:
#	docs/CHANGELOG.txt

Merge branch 'master' into viewport ...

# Conflicts:
#	docs/CHANGELOG.txt
#	examples/imgui_impl_win32.cpp
#	imgui_demo.cpp