Replace "master" with "controller" and "slave" with "peripheral" in
comments, errors, and debug messages.
Add CONTROLLER and PERIPHERAL constants to pyb.SPI and pyb.I2C classes;
retain MASTER and SLAVE constants for backward compatiblity.
The aim here is to have spi.c contain the low-level SPI driver which is
independent (not fully but close) of MicroPython objects and methods, and
the higher-level bindings are separated out to pyb_spi.c and machine_spi.c.
David P
Mike Causer
Jim Mussared
Damien George