APA: Refactor macros and support additional CSL variables

STYLE_DEVELOPMENT.md

@@ -191,15 +191,15 @@ The style title and ID are stored within the `<title/>` and `<id/>` elements nea
 For example:
 
 ```xml
-<title>American Psychological Association 6th edition</title>
+<title>APA Style 6th edition</title>
 <title-short>APA</title-short>
 <id>http://www.zotero.org/styles/apa</id>
 ```
 
 can be changed to:
 
 ```xml
-<title>American Psychological Association 6th edition - Modified</title>
+<title>APA Style 6th edition - Modified</title>
 <title-short>APA - modified</title-short>
 <id>http://www.zotero.org/styles/apa-modified</id>
 ```

apa-5th-edition.csl

@@ -1,8 +1,8 @@
 <?xml version="1.0" encoding="utf-8"?>
 <style xmlns="http://purl.org/net/xbiblio/csl" class="in-text" version="1.0" demote-non-dropping-particle="sort-only">
   <info>
-    <title>American Psychological Association 5th edition</title>
-    <title-short>APA (5th ed.)</title-short>
+    <title>APA Style 5th edition</title>
+    <title-short>Publication Manual of the American Psychological Association (5th ed.)</title-short>
     <id>http://www.zotero.org/styles/apa-5th-edition</id>
     <link href="http://www.zotero.org/styles/apa-5th-edition" rel="self"/>
     <link href="http://rdc.libguides.com/content.php?pid=63487" rel="documentation"/>