Hello world for the LowPowerTicker class

LED flip example with the help of LowPowerTicker

Revision:
0:3ef1e3fe0d3b
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mbed-os.lib	Mon Dec 04 00:53:19 2017 +0000
@@ -0,0 +1,1 @@
+https://github.com/armmbed/mbed-os/#182bbd51bc8d1b6217477c2b5de3f1d0c5e6249f