PlatformMutex class example - RTOS independent

Revision:
0:2084d9e90526
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mbed-os.lib	Thu Nov 30 22:14:35 2017 +0000
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+https://github.com/ARMmbed/mbed-os/#182bbd51bc8d1b6217477c2b5de3f1d0c5e6249f