slightly improved items/year plot
topic_report, first version

puts one topic keyword plot on each page
visualization: time averages & boxplots

these serve the topic_report

also moved the doc_topics_long function (so renamed) into topics_rmallet

source_all includes visualization.
topic_report now saves a bunch of png files

also: boxplot with proportions on log scale

bug in topic_keyword_plot remains
box plot and report tweaks