Adds fmtlib as 3rdparty dependency for easier string composition.

cmake/fmtlib.cmake

@@ -0,0 +1,20 @@
+include(FetchContent)
+
+FetchContent_Declare(
+	fmtlib
+	PREFIX "${CMAKE_BINARY_DIR}/deps"
+	DOWNLOAD_DIR "${CMAKE_SOURCE_DIR}/deps/downloads"
+	DOWNLOAD_NAME fmt-8.0.1.tar.gz
+	URL https://github.com/fmtlib/fmt/archive/8.0.1.tar.gz
+	URL_HASH SHA256=b06ca3130158c625848f3fb7418f235155a4d389b2abc3a6245fb01cb0eb1e01
+)
+
+if (CMAKE_VERSION VERSION_LESS "3.14.0")
+	FetchContent_GetProperties(fmtlib)
+	if (NOT fmtlib_POPULATED)
+		FetchContent_Populate(fmtlib)
+		add_subdirectory(${fmtlib_SOURCE_DIR} ${fmtlib_BINARY_DIR})
+	endif()
+else()
+	FetchContent_MakeAvailable(fmtlib)
+endif()