* Update unit tests to use generic perimeter
* Update solution to use perimeter
Update solution to use the generic term perimeter instead of circumference
I suggest to clarify that you only need to implement `From` and nobody really implements `Into` as soon as `From` is implemented.
I decided to add a separate paragraph after the `i8` and `i16` example, as they provide intuitive understanding of reverse relationship between `From` and `Into`. Alternatively trying to explain `From` and `Into` in generic way sounds more confusing than just adding this sentence after the specific example.
I found the phrasing confusing. Mentionning that a class implements From and then using `into()` seems confusing. It looks like that you meant that it implements `Into`.
So I believe that a little more details may help show why this exercise is valid.
I would have considered clarifying that `into` does not need to specify that we use the implementation for `i16` thanks to type analysis, but I assume this would add too much text, and this can either be ignored by the reader for the time being, or guessed
