Change from "Highlighting" to "Syntax Highlighting"

- change the title attribute in programing-languages.md
- change the title attribute in user-defined-language-system.md
- change the link names in README.md

Reason: The "Highlighting" in the User Manual sidebar might be misinterpreted as the various features controlled by Settings>Preferences>Highlighting, whereas if they are named "syntax highlighting", it removes ambiguity

README.md

@@ -14,8 +14,8 @@ Summary
 * [Sessions, Workspaces, and Projects](content/docs/session.md)
 * [Function List](content/docs/function-list.md)
 * [Auto-Completion](content/docs/auto-completion.md)
-* [Highlighting - Built-in Languages](content/docs/programing-languages.md)
-* [Highlighting - User Defined Languages](content/docs/user-defined-language-system.md)
+* [Syntax Highlighting - Built-in Languages](content/docs/programing-languages.md)
+* [Syntax Highlighting - User Defined Languages](content/docs/user-defined-language-system.md)
 * [Macros - Task Automation](content/docs/macros.md)
 * [Running External Commands](content/docs/run-menu.md)
 * [Plugins](content/docs/plugins.md)

content/docs/programing-languages.md

@@ -1,5 +1,5 @@
 ---
-title: Highlighting - Built-in Languages
+title: Syntax Highlighting - Built-in Languages
 weight: 70
 ---
 

content/docs/user-defined-language-system.md

@@ -1,5 +1,5 @@
 ---
-title: Highlighting - User Defined Languages
+title: Syntax Highlighting - User Defined Languages
 weight: 80
 ---