added STM32 support

[Arduino] / hardware / Arduino_STM32

diff --git a/hardware/Arduino_STM32 b/hardware/Arduino_STM32
new file mode 160000 (submodule)
index 0000000..501da92
--- /dev/null
+++ b/hardware/Arduino_STM32
@@ -0,0 +1 @@
+Subproject commit 501da92986e3885ac4c51fb05e4f84e342bed7ea