Improve Raspberry Pi support.

[abarisani]

This PR improves raspberry pi support by:

• making the code more consistent with the rest of the codebase
• making the pi specific packages more consistent among themselves
• removing unused functions or duplicate constants
• adding missing documentation
• fixing broken linkx
• adding required copyright and licensing notes

[abarisani]

@kenbell can you take a look?

[kenbell]

@abarisani - sure. I didn't get a chance today. I'll take a look over at the weekend.

[kenbell]

Thanks for updates. Pi2 seems to be working fine. PiZero I'm seeing corrupt output on the UART - I'll take a look.

[abarisani]

Thanks for updates. Pi2 seems to be working fine. PiZero I'm seeing corrupt output on the UART - I'll take a look.

Ok, I'll wait for the update on the PiZero before merging then. Thanks!