Adding IPv4 validator.

routersploit/exceptions.py

 class RoutersploitException(Exception):
     pass
+
+
+class OptionValidationError(RoutersploitException):
+    pass
\ No newline at end of file

routersploit/validators.py

+import socket
+
+from .exceptions import OptionValidationError
+
+
 def url(address):
     """Sanitize url.
 
@@ -7,3 +12,18 @@ def url(address):
         return address
     else:
         return "http://{}".format(address)
+
+
+def ipv4(address):
+    try:
+        socket.inet_pton(socket.AF_INET, address)
+    except AttributeError:
+        try:
+            socket.inet_aton(address)
+        except socket.error:
+            raise OptionValidationError("Option have to be valid IP address.")
+        return address.count('.') == 3
+    except socket.error:
+        raise OptionValidationError("Option have to be valid IP address.")
+
+    return address
\ No newline at end of file