Improve documentation

Hi Mikeal,

With this PR, i'm trying to improve the library documentation:

* Make the README lighter with only headlines about the library
* Move the advanced documentation into a "documentation" folder with it's own index
* Add many links to definition / datasheet for the boards, chips, drivers and protocols.
* Split the install process to a "step by step"
* Move the changelog a separated file

By doing this, i think it will ease the learning process, increase library SEO and make the documentation more "maintainable".

Cheers,

Jérémy