zsh completion for file arguments can be improved

• 372baf4dd4548db52d8f62d9e727d147c491cad7
• zsh: 5.9

make target/debug/uudoc
# e.g.
./target/debug/uudoc completion cat zsh

The snippet above prints

     5  _cat() {
…
    35  '-h[Print help]' \
    36  '--help[Print help]' \
    37  '-V[Print version]' \
    38  '--version[Print version]' \
    39  '::file:_files' \
    40  && ret=0
    41  }

• it is preferable to prepend (- *) to -h, --help, -V, and --version to stop further completion
• * should be prepended to ::file:_files to complete multiple files

At the moment cat, b2sum, chmod, and so forth completes a single file only.

Build target/debug/uudoc and run the provided completion command for zsh, then inspect how completion definitions are generated for cat, b2sum, and chmod. Done means the generated zsh snippet prevents option completion after a file argument and supports completing multiple files.