syntax_color: Add an enum value ENVENTOR_SYNTAX_COLOR_LAST

Add an enum value ENVENTOR_SYNTAX_COLOR_LAST to help to indicate the last enum value of the syntax color.

src/lib/Enventor_Legacy.h

@@ -51,7 +51,8 @@ typedef enum {
    ENVENTOR_SYNTAX_COLOR_SUB_KEYWORD,
    ENVENTOR_SYNTAX_COLOR_CONSTANT,
    ENVENTOR_SYNTAX_COLOR_SCRIPT_FUNC,
-   ENVENTOR_SYNTAX_COLOR_SCRIPT_KEYWORD
+   ENVENTOR_SYNTAX_COLOR_SCRIPT_KEYWORD,
+   ENVENTOR_SYNTAX_COLOR_LAST
 } Enventor_Syntax_Color_Type;
 
 EAPI int enventor_init(int argc, char **argv);