MAINT: update bibtex to author-year (#159)

* MAIN: update bibtex to author-year

* fix link checker mime warning

* fix typo

Author: mmcky

lectures/_config.yml

@@ -33,6 +33,7 @@ latex:
 sphinx:
   extra_extensions: [sphinx_multitoc_numbering, sphinxext.rediraffe, sphinx_tojupyter, sphinx_exercise, sphinx_togglebutton]
   config:
+    bibtex_reference_style: author_year
     linkcheck_ignore: ['https://doi.org/10.3982/ECTA8070',
                        'https://doi.org/10.1086/261749',
                        'https://doi.org/10.1086/262078',
@@ -69,6 +70,7 @@ sphinx:
        ['latex', 'text/html', 70],
        # Link Checker
        ['linkcheck', 'text/plain', 10],
+       ['linkcheck', 'text/html', 20],
      ]
     html_favicon: _static/lectures-favicon.ico
     html_theme: quantecon_book_theme