added experimental 7zip self extracting code

git-svn-id: svn://svn.code.sf.net/p/metalinks/code@834 84cd5247-9d1f-0410-ad08-ff3d2110de5e
added 7zS.sfx for self extracting archive, it is LGPL

git-svn-id: svn://svn.code.sf.net/p/metalinks/code@835 84cd5247-9d1f-0410-ad08-ff3d2110de5e