Merge commit 'f9801a968fb15cb74371f18a507c2004b852b4b6' as 'deps/imgui'

deps/imgui/examples/example_allegro5/README.md

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+
+# Configuration
+
+Dear ImGui outputs 16-bit vertex indices by default.
+Allegro doesn't support them natively, so we have two solutions: convert the indices manually in imgui_impl_allegro5.cpp, or compile dear imgui with 32-bit indices.
+You can either modify imconfig.h that comes with Dear ImGui (easier), or set a C++ preprocessor option IMGUI_USER_CONFIG to find to a filename.
+We are providing `imconfig_allegro5.h` that enables 32-bit indices.
+Note that the backend supports _BOTH_ 16-bit and 32-bit indices, but 32-bit indices will be slightly faster as they won't require a manual conversion.
+
+# How to Build
+
+### On Ubuntu 14.04+ and macOS
+
+```bash
+g++ -DIMGUI_USER_CONFIG=\"examples/example_allegro5/imconfig_allegro5.h\" -I .. -I ../.. main.cpp ../../backends/imgui_impl_allegro5.cpp ../../imgui*.cpp -lallegro -lallegro_main -lallegro_primitives -o allegro5_example
+```
+
+On macOS, install Allegro with homebrew: `brew install allegro`.
+
+### On Windows with Visual Studio's CLI
+
+You may install Allegro using vcpkg:
+```
+git clone https://github.com/Microsoft/vcpkg
+cd vcpkg
+bootstrap-vcpkg.bat
+vcpkg install allegro5 --triplet=x86-windows	; for win32
+vcpkg install allegro5 --triplet=x64-windows	; for win64
+vcpkg integrate install						    ; register include / libs in Visual Studio
+```
+
+Build:
+```
+set ALLEGRODIR=path_to_your_allegro5_folder
+cl /Zi /MD /I %ALLEGRODIR%\include /DIMGUI_USER_CONFIG=\"examples/example_allegro5/imconfig_allegro5.h\" /I .. /I ..\.. main.cpp ..\..\backends\imgui_impl_allegro5.cpp ..\..\imgui*.cpp /link /LIBPATH:%ALLEGRODIR%\lib allegro-5.0.10-monolith-md.lib user32.lib
+```