Revise the Raspberry Pi Pico sample implementation

[dgoffredo]

I'm using the SCD41 with a Raspberry Pi Pico W, and used this repository's sample implementation as a starting point.

The code in sample-implementations/RaspberryPi_Pico/ has several shortcomings that I aim to correct in this pull request:

• Rename CMakeLists.txt to have the proper casing.
• Refer to source and header files relative to the example's directory.
• Fix syntax errors in main.c.
• Fix bugs in main.c.
• Add logging.
• Add documentation.

This is my first time contributing to this project, so I'm happy to make any changes requested.