Exercise order: string before struct

[ephetic]

The struct exercises rely on knowledge learned in the string exercises, so should follow rather than precede them.

[ephetic]

Just discovered result1.rs comes long after errorsn.rs which clearly extends it. This PR maybe needs to be closed in favor of a broader review of exercise order.

[floriantz]

I am currently in the process of going through exercises for the first time as I wanted some practice writing rust code, and I had the same reflection.

Following the compiler I instinctively ended up using &str for the c and tuple struct, which then led me to introducing lifetimes. And using borrowed time for a struct like this doesn't really seems like a good pattern to me.

After some research I've eventually used String before even getting to the strings exercises that would have helped a lot.

Also since the quizz2 ends the Strings exercise it should probably be moved just after them in the PR.

[AbdouSeck]

Hi all, I am closing this PR in favor of #541. Struct before String is a bit hard to wrap one's head around. But remember that the String type in rust is a fat pointer to some buffer of data. You can use String typed data without having to know anything about how they behave. So, it would make sense to use them in structs before really understanding how they work.