Pim-dm

Support for defining the specific unicast and multicast routing tables identifier.
To define which table identifier to use for setting multicast trees and for RPF checks and getting unicast metrics, new global variables were defined on pimdm/tree/globals.py

This version brings IPv6 support:
- Implementation of IPv6 multicast routing interaction with Linux kernel;
- IPv4/IPv6 control packets' fields;
- IPv6 PIM interface;
- MLDv1 support;
- Interaction with IPv6 unicast routing table.

Fix exception in case log folders already exist

Use -li to check if StateRefresh is enabled

Previously, whenever a PIM-DM interface was added with StateRefresh capability enabled/disabled, to change this setting it was required to remove the interface and then add it again with the intended setting. For example:
`pim-dm -ai eth0`
`pim-dm -ri eth0`
`pim-dm -aisr eth0`
Now it is possible to change this capability without needing to remove the interface. For example:
`pim-dm -ai eth0`
`pim-dm -aisr eth0`

add keywords to PyPi.org project