MAINTENANCE: Automated closing of pull requests.

This commit exists to close the following pull requests on Github:

Closes #2883 (close requested by 'pwendell')
Closes #3364 (close requested by 'pwendell')
Closes #4458 (close requested by 'pwendell')
Closes #1574 (close requested by 'andrewor14')
Closes #2546 (close requested by 'andrewor14')
Closes #2516 (close requested by 'andrewor14')
Closes #154 (close requested by 'andrewor14')