kill the hardlinks found across the mdbook documentations.

[kiarie404]

To do this, search for the word 'hard links' across the src folders of the 2 mdbooks.
The point is to substitute these hard links with relative links for the sake of making the mdbooks future-proof.

example of hard link : "https://github.com/RustaceansKenya/driver-development-book/tree/master/driver_code "
example of equivalent soft link : "/driver_code"

The links should also work