Add most commonly used Doxygen comment snippets

snippets/c.snippets

@@ -4,3 +4,13 @@ snippet main
 	int main(${1:int argc, const char **argv}) {
 		$0
 	}
+
+# Doxygen
+snippet b
+	@brief ${0:desc}
+
+snippet r
+	@return ${0:desc}
+
+snippet rv
+	@retval ${1:val} ${0:desc}