Add ContainerOptionsBuilder::privileged()

[imp]

This adds new ContainerOptionsBuilder method privileged() to enable running privileged docker containers. I think it should be mentioned in CHANGELOG.md. Also, this could be potentially an incompatible change, since API addition is considered an incompatible change in semver universe.

The implementation is pretty straightforward, - the privileged field is already present in HostConfig, so there is only a new builder option to set the field to a required value.

As a side note - I have followed the precedence set by auto_remove() that gets a boolean argument. However, if I was to implement it from the scratch I'd choose to drop the boolean argument completely (similarly to the docker command line - you only mention it if you need it).

Fixes #148

[softprops]

@imp this branch seems to have a conflict with master. if you pull merge in latest Ill merge here

[imp]

@softprops rebased

[softprops]

published a new release including this pr https://github.com/softprops/shiplift/blob/master/CHANGELOG.md#050