SD card file helloworld demo using new mbed RTOS ver 5 file driver setup. Pins setup for LPC1768 - read comment in code about project's json file requirements for adding the SD filesystem driver

SD card r/w demo for mbed OS version 5 on LPC1768.

File drivers are added in json file with "target.components_add": ["SD"] for use in most recent OS 5 version.

Test messages are sent to serial port with printf's.

Revision:
0:3588d7473dce
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/tests/README.md	Wed Sep 11 12:39:11 2019 +0000
@@ -0,0 +1,12 @@
+# Testing examples
+
+Examples are tested using tool [htrun](https://github.com/ARMmbed/mbed-os-tools/tree/master/packages/mbed-host-tests) and templated print log. 
+
+To run the test, use following command after you build the example:
+```
+mbedhtrun -d D: -p COM4 -m K64F -f .\BUILD\K64F\GCC_ARM\blinky.bin --compare-log tests\blinky.log
+```
+
+
+More details about `htrun` are [here](https://github.com/ARMmbed/mbed-os-tools/tree/master/packages/mbed-host-tests#testing-mbed-os-examples).
+