Output of --help and --version have to go to stdout

To allow 'flowgrind -h | less' --help's and --version's output have to
go to stdout and not to stderr.
Merge branch 'next' of github.com:flowgrind/flowgrind into help-to-stdout
Merge pull request #168 from alexander-zimmermann/help-to-stdout

Output of --help and --version have to go to stdout