ENH: update to author_year bibtex style (#389)

Author: mmcky

lectures/_config.yml

@@ -34,6 +34,7 @@ latex:
 sphinx:
   extra_extensions: [sphinx_multitoc_numbering, sphinxext.rediraffe, sphinx_tojupyter, sphinxcontrib.youtube, sphinx.ext.todo, sphinx_exercise, sphinx_togglebutton, sphinx.ext.intersphinx, sphinx_reredirects]
   config:
+    bibtex_reference_style: author_year
     nb_mime_priority_overrides: [
        # HTML
        ['html', 'application/vnd.jupyter.widget-view+json', 10],