'XOR a memory region with a key
Usage:
MYNAME start end key'

def xormem(self, *arg):

    (start, end, key) = normalize_argv(arg, 3)
    if (key is None):
        self._missing_argument()
    result = peda.xormem(start, end, key)
    if (result is not None):
        msg('XORed    data    (first    32    bytes):')
        msg((('"' + to_hexstr(result[:32])) + '"'))
    return
