Add lightweight printf support

For now, printf() isn't hooked up to anything, but snprintf() can be
used to create a string to pass off to usart.tx_blocking().

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "firmware/ThirdParty/printf"]
+	path = firmware/ThirdParty/printf
+	url = https://github.com/mpaland/printf.git

firmware/Makefile

@@ -69,7 +69,7 @@ endif
 
 # Ignores dotfiles and other garbage some tools leave behind
 define find_important
-    $(shell find $(1) -type f -and -name $(2) -and -not -iname "*~" -and -not -iname "*#*" -and -not \( -path "*.cquery_cached_index*" \) -and -not \( -path "*build*" \) )
+    $(shell find $(1) -type f -and -name $(2) -and -not -iname "*~" -and -not -iname "*#*" -and -not \( -path "*.cquery_cached_index*" \) -and -not \( -path "*build*" \) -and -not \( -path  "*ThirdParty/printf/test/*" \) )
 endef
 
 FONTS        := small large_digits
@@ -118,10 +118,14 @@ CFLAGS += -ffreestanding
 CFLAGS += -fstack-usage -Wstack-usage=128
 # Defines
 CFLAGS += -D$(DEVICE_FAMILY_DEFINE) -D$(DEVICE_TYPE_DEFINE) -D$(DEVICE_LINE_DEFINE)
+CFLAGS += -DPRINTF_DISABLE_SUPPORT_FLOAT -DPRINTF_DISABLE_SUPPORT_EXPONENTIAL -DPRINTF_DISABLE_SUPPORT_PTRDIFF_T
+# Consider this one if we are running short on flash, it saved about 1K
+#CFLAGS += -DPRINTF_DISABLE_SUPPORT_LONG_LONG
 # Includes
 CFLAGS += -I./Bsp/Mcu/
 CFLAGS += -I./ThirdParty/stm32/$(DEVICE_LINE)/Include
 CFLAGS += -I./ThirdParty/CMSIS/Core/Include
+CFLAGS += -I./ThirdParty/printf
 CFLAGS += -I./build/gen/
 CFLAGS += -I.