tor/changes/ticket26481

  o Major features (new code layout):
   - Nearly all of Tor's source code has been moved around into more logical
     places.  The "common" directory is now divided into a set of libraries
     in "lib", and files in the "or" directory have been split into "core"
     (logic absolutely needed for onion routing), "feature" (independent
     modules in Tor), and "app" (to configure and invoke the rest of Tor).
     See doc/HACKING/CodeStructure.md for more information. Closes ticket
     26481.

     This refactoring is not complete: although the libraries have been
     refactored to be acyclic, the main body of Tor is still too
     interconnected.  We will attempt to improve this in the future.