Tweaked to run without 'article_metadata.pkl', cf.  #reuse_over_time &  ...

...#publish_vs_reuse

The make script trips up without article_metadata.pkl in two places:

figures/reuse_over_time.$(fig_format): scripts/reuse_over_time.py
data/reuse_estimates data/article_metadata.pkl

results/publish_vs_reuse: scripts/publish_vs_reuse.R data/keyword_matrix
(because the Python tries to load article_metadata.pkl)

To disable these lines I've commented out the appropriate terms in the
macros at the top of the script so they never get called.