Figure out what to do with the examples

[david-sawatzke]

I'd really like to keep them in there. They seem like good general representations and easily give an overview about how stuff is supposed to work. I'd remove the more specific ones (all the i2c & spi ones) and replace them with generalized versions (e.g. for spi a loopback example).

They provide quick example code which (even if they exist) are only partly given by doc tests. Especially for something like interrupts. They also serve as a way to have sample programs to compare binaries.

If we use a linker file with the minimum amount of memory and keep them in the CI system, I see little potential for breakage.

It also enables people that already have some chip, but not a specific board, get started, especially if they already have some experience in embedded c.

As we currently can't use doc tests, they also server as some form of build test.