Add submodule manager script (#523)

* Start on submodule manager, add STM32U0 submodule

* Submodule manager working!

* Fix if statement weirdness

* Auto add safe directory

* Get CMSIS headers from submodule as well

* Fix annoyance with multiple CMake configurations fighting over the venv dir

* Fix typo

* Set submodule 1 version back to test

* Revert "Set submodule 1 version back to test"

This reverts commit 7771d2c.

* Oops revert accidental hash change

Author: multiplemonomials

.gitmodules

@@ -1,3 +1,9 @@
 [submodule "doxygen-awesome-css"]
 	path = tools/doxygen-awesome-css
 	url = https://github.com/jothepro/doxygen-awesome-css.git
+[submodule "targets/TARGET_STM/TARGET_STM32U0/STM32Cube_FW/stm32u0xx-hal-driver"]
+	path = targets/TARGET_STM/TARGET_STM32U0/STM32Cube_FW/stm32u0xx-hal-driver
+	url = https://github.com/STMicroelectronics/stm32u0xx-hal-driver.git
+[submodule "targets/TARGET_STM/TARGET_STM32U0/STM32Cube_FW/cmsis-device-u0"]
+	path = targets/TARGET_STM/TARGET_STM32U0/STM32Cube_FW/cmsis-device-u0
+	url = https://github.com/STMicroelectronics/cmsis-device-u0.git