Better documentation of rng and prelude

[jounathaen]

This adds doc comments to the rng and prelude module as well as to the re-export of the svd2rust API.

The rng documentation might repeat some information, but as the generated documentation splits this to multiple pages, I find it is better that way. I also added small example code to the documentation. The examples in the repository are nice, but I personally would favor examples inside the docs.

It might be good, if somebody reads over the prelude part to check that I'm not completely off-track there.

[jounathaen]

Ok, apparently a changelog entry is missing. Is this necessary in this case?

[therealprof]

Ok, apparently a changelog entry is missing. Is this necessary in this case?

Why not? Improved documentation is noteworthy.

[jounathaen]

Ok, from my side this is ready for review.
I hope this is acceptable and helps somebody. Thank you all for your work on this project!
🙂

[burrbull]

Rebase, please.

[jounathaen]

Rebased!

[burrbull]

bors r+

[bors]

Build succeeded:

• ci (stm32f401, stable)
• ci (stm32f405, stable)
• ci (stm32f407, stable)
• ci (stm32f410, stable)
• ci (stm32f411, stable)
• ci (stm32f412, stable)
• ci (stm32f413, stable)
• ci (stm32f415, stable)
• ci (stm32f417, stable)
• ci (stm32f423, stable)
• ci (stm32f427, stable)
• ci (stm32f429, stable)
• ci (stm32f437, stable)
• ci (stm32f439, stable)
• ci (stm32f446, stable)
• ci (stm32f469, stable)
• ci (stm32f479, stable)
• Rustfmt