Improve the Traits section of the reference.

Author: Nick Hamann

src/doc/reference.md

@@ -1308,7 +1308,7 @@ type of the value is not required to ascribe to `Sync`.
 ### Traits
 
 Traits are Rust's take on interfaces. A _trait_ describes a collection of
-methods and associated items (like associated types or associated constants).
+methods and associated items (like associated functions, types, or constants).
 
 An example is the following trait `Shape`:
 
@@ -1323,14 +1323,15 @@ trait Shape {
 
 This defines a trait with two methods, `draw` and `bounding_box`. These
 methods can be invoked on any value whose type has an
-[implementation](#implementations) of this trait. The [method call
+[implementation](#implementations) of this trait, provided that the trait is in
+scope (via a `use` declaration if necessary). The [method call
 syntax](#method-call-expressions) looks like this: `value.bounding_box()`.
 
-Trait methods can be defined to take a [`self` type](#self-types) as a
-parameter. In the example above, each method takes `&self` as its first
-parameter. This is sometimes called the _receiver_ of the method, and indicates
-that for any type `T` implementing `Shape`, invoking one of the `Shape` methods
-will immutably borrow the `T` value for the duration of the method call.
+Trait methods take a [`self` type](#self-types) as a parameter. In the example
+above, each method takes `&self` as its first parameter. This is sometimes
+called the _receiver_ of the method, and indicates that for any type `T`
+that implements `Shape`, invoking one of the `Shape` methods will immutably
+borrow the `T` value for the duration of the method call.
 
 Traits can include default implementations of methods, as in:
 
@@ -1346,9 +1347,9 @@ Here the `baz` method has a default implementation, so types that implement
 `Foo` need only implement `bar`. It is also possible for implementing types
 to override a method that has a default implementation.
 
-It is not required that trait methods use a `self` type as a parameter. Methods
-that lack `self` types are called _static methods_. A common use for static
-methods is defining constructors, as the following example illustrates:
+Functions in a trait that do not take a `self` type as a parameter are called
+_associated functions_. A common use for associated functions is defining
+constructors, as the following example illustrates:
 
 ```
 trait Num {