Added C++ syntax highlighting

doc/coding.md

@@ -5,8 +5,9 @@ Please be consistent with the existing coding style.
 
 Block style:
 
-	bool Function(char* psz, int n)
-	{
+``` cpp
+bool Function(char* psz, int n)
+{
     // Comment summarising what this section of code does
     for (int i = 0; i < n; i++)
     {
@@ -18,7 +19,8 @@ Block style:
 
     // Success return is usually at the end
     return true;
-	}
+}
+```
 
 - ANSI/Allman block style
 - 4 space indenting, no tabs