stdout compression auto detection

[esteinig]

Auto detection of compression when writing to stdout is currently not implemented. It can be activated when specifying the --output-type|-O argument. It would be better for consistency to enable auto detection on stdout.

# do not run, output not compressed
nanoq -i test.fq > test.fq.gz

# do run, output compressed
nanoq -i test.fq -o test.fq.gz

# do run, output compressed
nanoq -i test.fq -O g > test.fq.gz