example of i2c slave device supporting block transfers

Dependencies:   lib_i2c_slave_block

Tested on nucleo board as slave. Use with i2c_master_block_example on raspberry pi as master.

Master I2C write will print on serial terminal 115200. User button will raise an irq; the RPi test program will service the interrupt.

See lib_i2c_slave_block for explanation of code.

Revision:
0:3ccfaf358115
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mbed-os.lib	Fri Jan 18 14:36:09 2019 -0800
@@ -0,0 +1,1 @@
+https://github.com/ARMmbed/mbed-os/#a8f0c33eaa2c52babff9655417c36f4b5edd54d7