added modules `collections` and `operator` to `pwn.toplevel`.
changed `pwnlib.util.safeeval.expr_eval/const_eval` to `pwnlib.util.safeeval.exrp/const`.
`pwnlib.tubes.tube.shutdown()` now accepts "in", "out", "recv", "send", "read" and "write";  subclasses should now implement `shutdown_raw()`.