Follow edition formatting for keywords

This updates the keywords chapter to follow our style guide where the
main text is supposed to describe the current edition, with admonitions
that describe differences to previous editions.

Author: ehuss

src/keywords.md

@@ -27,10 +27,13 @@ r[lex.keywords.strict.list]
 The following keywords are in all editions:
 
 - `as`
+- `async`
+- `await`
 - `break`
 - `const`
 - `continue`
 - `crate`
+- `dyn`
 - `else`
 - `enum`
 - `extern`
@@ -63,11 +66,12 @@ The following keywords are in all editions:
 - `while`
 
 r[lex.keywords.strict.edition2018]
-The following keywords were added beginning in the 2018 edition.
-
-- `async`
-- `await`
-- `dyn`
+> [!EDITION-2018]
+> The following keywords were added in the 2018 edition:
+>
+> - `async`
+> - `await`
+> - `dyn`
 
 r[lex.keywords.reserved]
 ## Reserved keywords
@@ -84,23 +88,23 @@ r[lex.keywords.reserved.list]
 - `box`
 - `do`
 - `final`
+- `gen`
 - `macro`
 - `override`
 - `priv`
+- `try`
 - `typeof`
 - `unsized`
 - `virtual`
 - `yield`
 
 r[lex.keywords.reserved.edition2018]
-The following keywords are reserved beginning in the 2018 edition.
-
-- `try`
+> [!EDITION-2018]
+> The `try` keyword was added as a reserved keyword in the 2018 edition.
 
 r[lex.keywords.reserved.edition2024]
-The following keywords are reserved beginning in the 2024 edition.
-
-- `gen`
+> [!EDITION-2024]
+> The `gen` keyword was added as a reserved keyword in the 2024 edition.
 
 r[lex.keywords.weak]
 ## Weak keywords