Change the wording of at-rules in PHPDoc

At-rules should be written as "`at-rules`", not as "`@-rules`", as the
`@` character is used to mark PHPDoc annotations.

(In addition, the naming then is consistent with the terminology
used at https://developer.mozilla.org/en-US/docs/Web/CSS/Syntax.)

Author: oliverklee

src/CSSList/AtRuleBlockList.php

@@ -6,7 +6,7 @@
 use Sabberworm\CSS\Property\AtRule;
 
 /**
- * A BlockList constructed by an unknown @-rule. @media rules are rendered into AtRuleBlockList objects.
+ * A BlockList constructed by an unknown at-rule. @media rules are rendered into AtRuleBlockList objects.
  */
 class AtRuleBlockList extends CSSBlockList implements AtRule
 {

src/CSSList/CSSList.php

@@ -23,7 +23,7 @@
 
 /**
  * A CSSList is the most generic container available. Its contents include RuleSet as well as other CSSList objects.
- * Also, it may contain Import and Charset objects stemming from @-rules.
+ * Also, it may contain Import and Charset objects stemming from at-rules.
  */
 abstract class CSSList implements Renderable, Commentable
 {

src/CSSList/Document.php

@@ -8,7 +8,7 @@
 
 /**
  * The root CSSList of a parsed file. Contains all top-level css contents, mostly declaration blocks,
- * but also any @-rules encountered.
+ * but also any at-rules encountered.
  */
 class Document extends CSSBlockList
 {

src/OutputFormat.php

@@ -54,7 +54,7 @@ class OutputFormat
     public $sSpaceBetweenBlocks = "\n";
 
     /**
-     * Content injected in and around @-rule blocks.
+     * Content injected in and around at-rule blocks.
      *
      * @var string
      */

src/RuleSet/AtRuleSet.php

@@ -6,7 +6,7 @@
 use Sabberworm\CSS\Property\AtRule;
 
 /**
- * A RuleSet constructed by an unknown @-rule. `@font-face` rules are rendered into AtRuleSet objects.
+ * A RuleSet constructed by an unknown at-rule. `@font-face` rules are rendered into AtRuleSet objects.
  */
 class AtRuleSet extends RuleSet implements AtRule
 {