Added fmt as a submodule

.gitmodules

fmt

fmt/CMakeLists.txt

fmt/include/fmt/chrono.h

fmt/include/fmt/color.h

fmt/include/fmt/compile.h

fmt/include/fmt/core.h

fmt/include/fmt/format-inl.h

fmt/include/fmt/format.h

fmt/include/fmt/locale.h

fmt/include/fmt/os.h

fmt/include/fmt/ostream.h

fmt/include/fmt/posix.h

fmt/include/fmt/printf.h

fmt/include/fmt/ranges.h

fmt/src/format.cc

fmt/src/os.cc