Breaking changes for most users! ...

Added an extra 'void* renderer_user_data' parameter to ImDrawCallback (stored in ImDrawCmd::UserCallback). This allows custom rendering back-ends to pass custom local rendering information to the callback.
IF YOU USE AN OLD RENDERER BACK-END OR COPIED A RENDERER BACK-END BEFORE 1.71, YOUR COMPILATION WILL FAIL ON THIS LINE:
     pcmd->UserCallback(cmd_list, pcmd);
You can fix it by adding a trailing NULL parameter:
     pcmd->UserCallback(cmd_list, pcmd, NULL);
If your back-end needs to support multiple versions, you can use a '#if (IMGUI_VERSION_NUM >= 17004)' test.

Examples/Backends: Metal: Added support for large meshes (64k+ vertices) with 16-bits indices, enable 'ImGuiBackendFlags_HasVtxOffset' config flag in back-end. (#2591, #2592)

Examples: Added missing per-renderer local changelogs. (#2037, #1639, #2452)

ImDrawCallback_ResetRenderState: Added Metal.

Clarified asserts comments + todo entries. (#2500)

Tabs to Spaces, comments.

Fix typos. (#2413)

Examples: Metal: Compilation fix.

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)

Removed trailing spaces (#2038, #2299)

Examples: Downgrading projects to xcode 9.2 (maybe 8.0) (#2134) ...

* example_apple_opengl2: The deployment target was set to 10.12 from XCode 9.2.
* imgui_impl_metal: header not found by XCode 9.2.
* example_apple_metal: The deployment target was set to 10.12 from XCode 9.2.

About, IO: Added io.BackendPlatformName, io.BackendRendererName for informational/QA purpose.

Examples: Using "dear imgui" terminology in all examples headers/comments + fix minor typo.

Examples: Cast to ImTextureID instead of void* when assigning to TexId. Applied to all examples. (#2015)

Examples: Comments + shallow coding convention tweak to be consistent across examples and with imgui_impl_osx

Apple: Fixed example_osx_opengl2, renamed to example_apple_opengl2 + misc comments

Introduced a new Metal renderer implementation and a new example illustrating usage of Metal on macOS and iOS (partially addresses #1873)