Create TODO.md

TODO.md

+In the years since I wrote this, docker and friends exploited namespaces to create much more complex frameworks than this. A good side effect is that iproute2 learnt to manage namespaces with some very useful commands. Also, a functioning python library to talk to NETLINK was published.
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+Nemu would get a big performance and reliability improvement from adopting those:
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+* [Python Netlink library](https://pypi.python.org/pypi/pyroute2)
+* [IProute2 namespace management](http://baturin.org/docs/iproute2/#Network%20namespace%20management)
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+Another requested feature is to isolate the bridge interface from the default namespace, which was not possible a few years ago. I will have to research this again.