Add rtos_basic sample from mbed site

I pulled this RTOS sample from
  https://developer.mbed.org/teams/mbed/code/rtos_basic/

I added it since I recently broke building of RTX for Cortex-M0+ parts
such as the KL25Z and didn't notice since only some LPC1768 samples
were previously making use of the RTOS.

Thanks to @rosterloh for pointing this issue out:
https://github.com/adamgreen/gcc4mbed/issues/20
Fix for issue #20

When filtering out unsupported TARGET_M0 targets, it was also filtering
out the desired TARGET_M0P target.

The filtering is now peformed with the */TARGET_XX/* pattern instead of
the previous */TARGET_XX* pattern previously used.  This did require
placing a trailing slash on the input directory names just before
performing this pattern match and then removing it immediately
thereafter since the rest of the code doesn't want the trailing
slashes.