Hx711-multi

converted hx711 logging to be specific to hx711-multi instead of generic 'logging' call

- added separate function for zeroing so that we can do it manually if needed
- renamed some functions and variables for clarity
- changed load cell failure to warning since sometimes they will all fail due to clocking, but will work during the next iteration

Working release after a few small bug changes since initial release yesterday.
* decreased standard deviation limit to 100 instead of 1000. I was seeing some instances where the bad data (coming from a sensor that isn't connected) just got lucky with being close to each other. The good sensors I am using usually only have a stdev of ~20-30.
* added 400ms sleep after a channel config change or power-up, per documentation for settling time
* reorganized test scripts as they were partially written while testing locally without the pip package
* fixed typo in readme