[ ] stop using the st-mark thing
[ ] doc.add_stream { |st| st.bt ... }

[o] st = d.addstream
    st.tf '/helv', 12
    st.bt 5, 6, "hello"
    d.write('out.pdf') # closes the stream...
[ ] fail if insert_content or insert_font on an unclosed stream obj

[ ] recompress idea? uncompress with pdftk, recompress with podoff
    smaller docs anyway...