rn2903: Initial implementation; C; C++ wraps C; examples

This requires a new MRAA with UART sendbreak support.

Signed-off-by: Jon Trulson <jtrulson@ics.com>

src/rn2903/CMakeLists.txt

@@ -0,0 +1,8 @@
+upm_mixed_module_init (NAME rn2903
+    DESCRIPTION "LoRaWAN transceiver"
+    C_HDR rn2903.h rn2903_defs.h
+    C_SRC rn2903.c
+    CPP_HDR rn2903.hpp
+    CPP_SRC rn2903.cxx
+    CPP_WRAPS_C
+    REQUIRES mraa utilities-c)