Add files.flattenNestedTree() to unnest dir tree
Add files.flattenNestedTree() to unnest dir tree

* From path:to:file:content to path:content
maryrosecook/gitlet,harrytruong/gitlet,pysnow530/gitlet,pirafrank/gitlet,pirafrank/gitlet,maryrosecook/gitlet,harrytruong/gitlet