Add docs for custom Jinja filter functions.
Add docs for custom Jinja filter functions.

louisstow/dailygraphics,stlpublicradio/dailygraphics,wjcjenny/dailygraphics,nprapps/dailygraphics,swastvedt/dailygraphics,abcnews/dailygraphics,nprapps/dailygraphics,cerealcommas/mashgraphics,stlpublicradio/dailygraphics,louisstow/dailygraphics,abcnews/dailygraphics,cerealcommas/mashgraphics,BenHeubl/dailygraphics,swastvedt/dailygraphics,onyxfish/dailygraphics,swastvedt/dailygraphics,nprapps/dailygraphics,wjcjenny/dailygraphics,stlpublicradio/dailygraphics,onyxfish/dailygraphics,stlpublicradio/dailygraphics,cerealcommas/mashgraphics,louisstow/dailygraphics,BenHeubl/dailygraphics,nprapps/dailygraphics,BenHeubl/dailygraphics,wjcjenny/dailygraphics,onyxfish/dailygraphics,abcnews/dailygraphics,abcnews/dailygraphics