Update bundled retf.txt
Interpret text as Unicode rather than bytes

This fixes some regexps that contain Unicode characters and would
otherwise do unpredictable things.

It also allows us to detect and skip binary files.
Add command line option --quiet
Print unified diff instead of overwriting by default

For old behavior use the new --apply switch.

This is a much more user-friendly behavior since in most cases the
changes will need to be reviewed manually anyway. It also reduces the
chance of accidents.
Update README
Clarify CC-BY-SA licensing of Wikipedia content

Thanks to Matt Lee from GNU for reviewing this license statement.
implement processing over directories

topy can now take files and/or directories as arguments.  A simple walk
is performed over directories, ignoring hidden ones