sys.flags: switch from `BoxedSysFlags` to cpythons `PyStructSequence`

[Marius Wachtler]

our BoxedSysFlags is missing some stuff (e.g. __str__) I think it's better to remove it just use cpythons code for it.

[AN Long]

Hi @undingen I have a try on implement this on #1312 , can you have a look at it?

And I found these four flags is not implemented on pyston, so I just set them to 0, I don't know is this a right way:

int Py_DebugFlag = 0;
int _Py_QnewFlag = 0;
int Py_DontWriteBytecodeFlag = 0;
int Py_NoUserSiteDirectory = 0;

[Kevin Modzelewski]

Closed by #1312