Write output to stdout

[nichtich]

Is your feature request related to a problem? Please describe.

SVG output should be pipe-able.

Describe the solution you'd like

mmdc -i input.mmd -o - # emit SVG by default
mmdc -i input.mmd -e pdf -o - # emit PDF (if possible, I only need SVG)

Describe alternatives you've considered

I tried process substitution:

mmdc -i input.mmd -o >( tee output.svg )

but mmdc complains because the temporary output file in /dev/fd lacks file extension.

Manually creating a named pipe with mkfifo works, but this requires a more complex bash script:

mkfifo tmp.svg
cat tmp.svg | tee output.svg
mmdc -i input.mmd -o tmp.svg
rm tmp.svg