Ploy-virtualbox

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* Added documentation.
[fschulze]

* Renamed ``vb-master`` to ``virtualbox``, so the uids of instances are nicer.
[fschulze]

* Enable DHCP server when creating or modifying it.
[fschulze]

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* Verify and if possible create host only interfaces and dhcpservers.
[fschulze]

* Add support for instances that have manually been put into ``saved`` state.
[fschulze]

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* Packaging and test fixes.
[fschulze]

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* Python 3 compatibility.
[fschulze]

* Renamed mr.awsome to ploy and mr.awsome.virtualbox to ploy_virtualbox.
[fschulze]

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* Initial release
[fschulze]