title: What is the opposite of `git filter-branch --subdirectory-filter`?
body: <p>With <code>git filter-branch --subdirectory-filter</code> you can transform a subdirectory from the current repository into a repository on its own. What I'd like to do, however, is an opposite thing: create a repository that will contain the full contents of the current repository as a subdirectory, keeping the complete history as if they were always in that subdirectory. I don't want to use submodules, because I'd like that directory to be a completely integral part of the repository.</p>
  
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  <p>Background: I was tasked with writing a simple script, but the scope of task has been expanded, so now that script becomes just a subdirectory in a bigger project. It also has no point of living on it's own, so a solution without submodules is preferred.</p>