title: How do I manage two diverging codebases in git?
body: <p>I have a legacy codebase (Legacy), and a new codebase (New).  </p>
  
  <p>New will be based directly off legacy, but will eventually diverge down its own path.  Legacy will continue to to receive support.</p>
  
  <p>What is the best way to sync changes that are common between both codebases?</p>