[script] vector slicing, basic file functions

new operators:
vector(int, byte) - int -> works like py's list[0:-int]
vector(int, byte) : int -> works like py's list[int:]

new functions:
fileRead, fileWrite, fileExists, bytesToStr

source/script/types.h

@@ -57,7 +57,8 @@ enum Errors {
 	ERRNOVAR,
 	ERRNOFUNC,
 	ERRINACTIVEINDENT,
-	ERRDIVBYZERO
+	ERRDIVBYZERO,
+	ERRFATALFUNCFAIL,
 };
 
 enum Variables {