[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/fs/menus/filemenu.c

@@ -82,6 +82,8 @@ void RunScript(char *path, FSEntry_t entry){
     ctx.script = runLexar(script, size);
     free(script);
 
+    dictVectorAdd(&ctx.varDict, newDict(CpyStr("_CWD"), (newVar(StringType, 0, .stringType = path))));
+
     printError(mainLoop(&ctx));
 
     freeVariableVector(&ctx.varDict);