static type for Library.using: avoid Java 11 warnings on "Illegal reflective access";
more uses of "using";

avoid loading of font file, to eliminate "Illegal reflective access by com.lowagie.text.pdf.MappedRandomAccessFile$1 (iText-2.1.5.jar) to method java.nio.DirectByteBuffer.cleaner()" -- due to com.lowagie.text.pdf.TrueTypeFont.process() / RandomAccessFileOrArray;

more explicit Isabelle_Fonts.Entry;
more robust font embedding into PDF and HTML;

clarified modules;

tuned signature;

more JFreeChart operations;
tuned signature;

tuned;

provide FontMapper for embedded fonts;

support for PNG output;

write_pdf for JFreeChart;

file system operations for Graphics2D output;