[2.1] General code improvements & minor bug fixes

General code improvements & minor bug fixes.

How to update

1. Open the RPI Pico's console**
2. Type these commands:
   import storage
storage.remount("/", readonly=False)
   You are now able to write files to the RPI Pico.
3. Copy all content of the code.py file (included in the src zip of this release) to the code.py file on the RPI Pico.

** I expect that you've already installed Thonny. If not, install it and open the Pico's console by choosing it's port in the interpreter settings. You will find more info about that pretty much anywhere on the web.