More attributes improvements

Improve the flow of documentation by showing the definition on
the first sentence and then have what takes attributes be its own
paragraph later on.

Moar links of course.

Explain that the rest of the page after that will be descriptions
of attributes that are in use today.

Author: Havvy

src/attributes.md

@@ -21,26 +21,31 @@
 >    | _MetaItem_  
 >    | _MetaItem_ `,` _MetaSeq_
 
-Any [item declaration], [statement], [block expression] or
-[generic lifetime or type parameter][generics] may have an attribute applied to
-it. Attributes are modeled on Attributes in [ECMA-335], with the syntax coming
-from [ECMA-334]\ (C#). An _attribute_ is a general, free-form metadatum that is
-interpreted according to name, convention, and language and compiler version.
+An _attribute_ is a general, free-form metadatum that is interpreted according
+to name, convention, and language and compiler version. Attributes are modeled
+on Attributes in [ECMA-335], with the syntax coming from [ECMA-334]\ (C#).
+
 Attributes may appear as any of:
 
-* A single identifier, the attribute name
+* A single identifier, the _attribute name+
 * An identifier followed by the equals sign '=' and a literal, providing a
-  key/value pair
+  key-value pair
 * An identifier followed by a parenthesized literal, providing a
-  key/value pair
+  key-value pair
 * An identifier followed by a parenthesized list of sub-attribute arguments
 
 _Inner attributes_, written with a bang ("!") after the hash ("#"), apply to the
-item or block expression that the attribute is declared within. _Outer
-attributes_, written without the bang after the hash, apply to the thing that
-follows the attribute.
+thing that the attribute is declared within. _Outer attributes_, written without
+the bang after the hash, apply to the thing that follows the attribute.
+
+Any [item declaration], [statement], [block expression] or
+[generic lifetime or type parameter][generics] may have an attribute applied
+to it. Statemetns and generic lifetime or type parameters can only take outer
+attributes while block expressions can only take inner attributes. All item
+declarations can take outer attributes while [external blocks], [functions],
+[implementations], and [modules] allow inner attributes.
 
-An example of attributes:
+Some examples of attributes:
 
 ```rust
 // General metadata applied to the enclosing module or crate.
@@ -63,6 +68,9 @@ mod bar {
 type int8_t = i8;
 ```
 
+The rest of this page will describe which attribute names that have meaning and
+their respective meaning.
+
 ## Crate-only attributes
 
 - `crate_name` - specify the crate's crate name.
@@ -545,4 +553,7 @@ You can implement `derive` for your own type through [procedural macros].
 [item declaration]: items.html
 [generics]: generics.html
 [statement]: statements.html
-[block expression]: expressions/block-expr.html
+[block expression]: expressions/block-expr.html
+[external blocks]: items/external-blocks.html
+[implementations]: items/implementations.html
+[modules]: items/modules.html