MAINTENANCE: Automated closing of pull requests.

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

Closes #3205 (close requested by 'srowen')
Closes #5478 (close requested by 'andrewor14')
Closes #4910 (close requested by 'srowen')
Closes #5080 (close requested by 'marmbrus')
Closes #537 (close requested by 'srowen')
Closes #5691 (close requested by 'srowen')
Closes #5469 (close requested by 'marmbrus')