Support UTF-8 in man pages

Tries to detect when the calling module includes `utf8.pm` and

- enables an `encoding(UTF-8)` flag with `Path::Class::File->spew()`

- inserts `=encoding UTF-8` as the first statement in the generated
  pod file

I am not a perl guru. So, this might be brittle, have unwanted side
effects and all other kinds of bad things happening, but it works
for me (TM).