Add a lime2 + mod-io relay switch on/off example.

examples/lime2-mod-io-relay-on_off.py

+#!/usr/bin/python3
+"""
+This is an example of connecting LIME2 + LIME2-SHIELD + MOD-IO (over UEXT) and controlling a relay (on / off).
+
+
+I. prepare lime2 + lime2's shield + MOD-IO
+
+# install packages
+root@t470:~/tmp$ apt install minicom
+
+ivan@t470:~/tmp$ wget http://images.olimex.com/release/a20/A20-OLinuXino-bionic-minimal-20200601-122736.img.7z
+ivan@t470:~/tmp$ 7z e A20-OLinuXino-bionic-minimal-20200601-122736.img.7z 
+# download from https://www.balena.io/etcher/
+ivan@t470:~/tmp$ unzip ../balena-etcher-electron-1.5.95-linux-x64.zip
+ivan@t470:~/tmp$ chmod o+x balenaEtcher-1.5.95-x64.AppImage
+ivan@t470:~/tmp$ ./balenaEtcher-1.5.95-x64.AppImage
+# flash to micro-sd card the previously download image
+
+# put micro-sd card inside lime2 (not shield!)
+
+# put lime2 shield on lime2 board
+
+# charge lime2 board with 5V adaptor
+
+# connect USB cable to USB1 on lime2 board and a laptop
+
+# wait till you see a green light at the board
+ivan@t470:~/tmp$ minicom -D /dev/ttyACM0
+
+# username and password are olimex / olimex 
+
+# put wifi dongle (or ethernet cable) but get an ipV4 address to ssh on
+
+ssh olimex@<ipv4_address> (password: olimex)
+
+# update software
+root@a20-olinuxino:~# apt update
+root@a20-olinuxino:~# apt upgrade
+root@a20-olinuxino:~# reboot now
+
+# XXX: had to set DNS in /etc/resolv.conf to 8.8.8.8 instead of 127.0.0.57
+
+# install python
+olimex@a20-olinuxino:~$ sudo bash
+root@a20-olinuxino:~# apt install python3
+root@a20-olinuxino:~# apt install python3-venv python3-pip
+root@a20-olinuxino:~# python3 -m pip install --upgrade pip setuptools wheel 
+root@a20-olinuxino:~# pip3 install pyA20Lime2
+
+# enable i2c-1 by running and selecting it (temporary step until fixed by Olimex)
+root@a20-olinuxino:~# olinuxino-overlay 
+
+# prove it's enabled by
+root@a20-olinuxino:~# i2cdetect -r 1  # should show  0х58 is available
+
+# connect MOD-IO through UEXT cable to UEXT2 at LIME2-SHIELD and power it (12V adapter)
+
+
+II. finally run this script as root, you should see RELAY1's led showing green color.
+
+"""
+
+from pyA20Lime2 import i2c
+i2c.init("/dev/i2c-1")
+i2c.open(0x58)
+
+# switch ON RELAY1
+i2c.write([0x10, 0x01])
+
+# switch OFF RELAY1
+i2c.write([0x10, 0x00])
+