Add nanofmt as submodule

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "components/nanofmt/nanofmt"]
+	path = components/nanofmt/nanofmt
+	url = https://github.com/antsouchlos/nanofmt.git

components/nanofmt/CMakeLists.txt

@@ -0,0 +1,2 @@
+idf_component_register(SRCS "nanofmt/src/serialize.cpp"
+        INCLUDE_DIRS "nanofmt/include")

main/src/main.cpp

@@ -13,6 +13,8 @@
 #include "esp_flash.h"
 #include "esp_system.h"
 
+#include "nanofmt/format.h"
+
 extern "C" void app_main(void)
 {
     printf("Hello world!\n");