Merge branch '2021-02-09-master-libi2c_import_only_on_linux' into 'master'

2021 02 09 master libi2c import only on linux

See merge request !9

i2c/I2C.py

+if os.sys.platform is 'linux':
     import pylibi2c;
 import time
 import logging

requirements.txt

-pylibi2c (github.com/amaork/libi2c)
+git+https://github.com/amaork/libi2c.git; platform_system == "linux"
 opcua
 numpy
 recordclass