MAINTENANCE: Automated closing of pull requests.

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

Closes #464 (close requested by 'JoshRosen')
Closes #283 (close requested by 'pwendell')
Closes #449 (close requested by 'pwendell')
Closes #907 (close requested by 'pwendell')
Closes #2478 (close requested by 'JoshRosen')
Closes #2192 (close requested by 'tdas')
Closes #918 (close requested by 'pwendell')
Closes #1465 (close requested by 'pwendell')
Closes #3135 (close requested by 'JoshRosen')
Closes #1693 (close requested by 'tdas')
Closes #1279 (close requested by 'pwendell')