Suggestion for chapter about bindings

[gor77]

Hi,

I feel variable bindings need to be explained more.

Working and learning alone, it took me quite some time to figure them out
(hopefuly I got everything right). Things like:

1. Keyword let declares a new binding - sort of linkage between name and value.
   It has to be used ONLY when you want to introduce a new binding:

fn main() {
    x = 2; // this is an error
}

1. You can have two or more bindings with the same name. The one declared
   last will "win" (or shadow) over the previous one

fn main() {
    let x = 2;
    let x = 3; //no error here, from now on x is 3
}

1. Each new binding can have its mutability independently declared,
   even if it has the same name as one before

fn main() {

    let x = 2;
    let mut x = 3; // from now on, x has value 3 and it can be changed

}

These things are simply not stressed enough in the book (or not mentioned at all) and understanding these things is the basis for understanding something like this:

let x = 2; // this is immutable binding and from now on we can't modify x
let mut x = x; // but when we create a new mutable binding with the same name
x = 3; //...then we can change x

[xiaochuanyu]

Just a note. Comparing to Rust By Example section about bindings, shadowing and declaring uninitialized bindings have been left out.