renamed Buffer.write to File.write_buffer; added scalable iterator fold_lines; tuned;
renamed Buffer.write to File.write_buffer;
added scalable iterator fold_lines;
tuned;

MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle