This "md" directory is a source directory for building html files in the
pd/doc/8.topics subdirectory (and hopefully later also in pd/doc/1.manual).  The
target files are built using the shell script "generate-html.sh" in this
directory.  (Later when/if there are many ".md" files here, this should be
replaced by a makefile.)

pandoc generates warnings about a missing document title when converting to
html - I can't figure out how to supporess this but don't want to have the
title appear in huge type at the top of the html output - perhaps we need to
override the HTML  output template via --template flag.

Source files for creating figures are also included here (svg and, later,
perhaps other file formats).  The target figures themselves are generated by
hand and moved into the html target directories in pd/doc.