suggestion: let - denote stdout for -o option

[dustymabe]

specifying - to the -o option creates a file named -. Could we let this actually mean stdout like it does for so many other applications. I know there is a --stdout flag but I think some people will probably not read that far (as I didn't) and go with -o - instead.

$ ../kompose -f docker-compose.yml convert -o -
$ ls -l
total 28
-rw-rw-r--. 1 vagrant vagrant 2832 Sep 25 15:56 -
-rw-rw-r--. 1 vagrant vagrant  538 Sep  6 21:42 docker-compose-bundle.dsb
-rw-rw-r--. 1 vagrant vagrant  132 Sep  6 21:42 docker-compose.yml
-rw-rw-r--. 1 vagrant vagrant 1729 Sep  6 21:42 docker-gitlab.yml
-rw-rw-r--. 1 vagrant vagrant  379 Sep  6 21:42 docker-guestbook.yml
-rw-rw-r--. 1 vagrant vagrant 1486 Sep 25 15:54 docker-voting-bundle.dsb
-rw-rw-r--. 1 vagrant vagrant  485 Sep 25 15:54 docker-voting.yml
$ ../kompose --version
kompose version 0.1.0 (fa46376)

[ngtuna]

@dustymabe you got it.