What is this

this is a example for mikke89/RmlUi#397

in this pr, add three option:

• RMLUI_FREETYPE_EXTERNAL: Use external FreeType instead of by find_package
• RMLUI_RLOTTIE_EXTERNAL: Use external RLOTTIE"
• RMLUI_LUA_EXTERNAL: Use external LUA, this ask RmlUi_External::Lua target be set

please read extern/CMakeLists.txt for more.

Build

git clone --recursive git@github.com:cathaysia/rmlui_externallib_example.git
cd rmlui_externallib_example
cmake -B build
cmake --build build