Add torrc.d configuration directory on deb packages

A torrc.d style configuration directory could be added to the debian packages for version 0.3.1.1-alpha and above. Since #1922 (moved) is now implemented, it is easy to add this feature.

I attempted to add this feature on this branch: https://github.com/Jigsaw52/debian-tor/tree/add-torrc.d

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