Introducing rtorrent-docker CI environment

[rakshasa]

• https://github.com/rakshasa/rtorrent-docker

While the steps to running the current (though limited) CI tests should be easy, rtorrent-docker has not been widely tested.

# On linux systems:
./rdo init default

# On non-linux systems creates a docker-machine based on rancheros:
./rdo init machine

# Start custom bash session:
./rdo bash

# In rdo bash seesion:
rdo git clone
rdo build all
rdo batch tests/ci-all

The intention is that all future changes to rtorrent should include tests, if possible.

[rakshasa]

ci-default
ci-low-diskspace
ci-nat
ci-throttle

The above four CI tests are now working, the next step is to add tests for IPv6.

As the rtorrent-docker test environment now has most of the features I need, implementing the tests for changes I'm making to the client should take much less time.