title: remove git submodule but keep files
body: <p>I have a git submodule that I would like to become part of my main project (since I have a lot of project specific code that will go into the submodule). </p>
  
  <p>So I'd like to remove the git references to the submodule and add the files to my main git repository.</p>
  
  <p>But how ?</p>