Defer the reading from and printing to the Serial port, to the global event queue.

Revision:
0:3a7d1a0a9b0b
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mbed-os.lib	Fri Nov 10 16:03:09 2017 +0000
@@ -0,0 +1,1 @@
+https://github.com/ARMmbed/mbed-os/#78474a5129e18e136cc7e872adbaa5b74fbb8f6a