support for advanced SPI functions

docs/reference/pins/spi-pins.md

@@ -0,0 +1,17 @@
+# SPI Pins
+
+Sets the SPI MOSI, MISO and SCK pins
+
+```sig
+pins.spiPins(DigitalPin.P0, DigitalPin.P1, DigitalPin.P2);
+```
+
+### Parameters
+
+* ``MOSI``, the ``MOSI`` pin
+* ``MISO``, the ``MISO`` pin
+* ``SCK``, the ``SCK`` pin
+
+### See also
+
+[SPI](https://developer.mbed.org/handbook/SPI)