GeezerVison

Adapting the project structure to the coreutils structure.

coreutils uses a source code tree, which has each tool in a separate dir unter /uu,
a separate library tree and the main file under /bin. Also a number of features are
available in another directory.

Adaptiong this structure allows more usage of the coreutils macros
and methods. It makes it easier for the developers to navigate when
working in both projects.

Each utility can now be opened standalone
which makes it also easier to test and benchmark.

Since it is a file location restructure, the commit is containing
a lot of files. All files were left unchanged as much as
possible and mostly the import locations were
changed.

Changes:

• A workspace is introduced, currently with the members
  uudiff (library) and the utilities uu/cmp and uu/diff.
• main.rs is now /bin/diffutils.rs
• the uumain method is now used as entry point to the utility
• all utilites have a separate folder under /uu
• Exitcodes are now i32 and push to
• coreutils only has License files for MIT
• args are now read by using uucore::args_os()
• context_diff and unified_diff now use TempDir
• benches are separated for each utility and
  have centralized support functions

Issues:

• The uucore::bin! macro needs to be implemented
  for all main functions. Currently missing
  internationalization.
• Tests must be run with "cargo test --workspace".
• Unclear, if features can be defined globally.
• Clarification of the Licenses needed.