MAINTENANCE: Automated closing of pull requests.

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

Closes #4994 (close requested by 'marmbrus')
Closes #4995 (close requested by 'marmbrus')
Closes #4491 (close requested by 'srowen')
Closes #3597 (close requested by 'srowen')
Closes #4693 (close requested by 'marmbrus')
Closes #3855 (close requested by 'marmbrus')
Closes #4398 (close requested by 'marmbrus')
Closes #4246 (close requested by 'marmbrus')
Closes #5153 (close requested by 'srowen')
Closes #3626 (close requested by 'srowen')
Closes #5166 (close requested by 'marmbrus')
Closes #5040 (close requested by 'marmbrus')
Closes #5044 (close requested by 'marmbrus')
Closes #5440 (close requested by 'JoshRosen')
Closes #4039 (close requested by 'marmbrus')
Closes #1237 (close requested by 'srowen')
Closes #216 (close requested by 'mengxr')
Closes #5092 (close requested by 'srowen')
Closes #5100 (close requested by 'marmbrus')
Closes #4469 (close requested by 'marmbrus')
Closes #5246 (close requested by 'srowen')
Closes #5013 (close requested by 'marmbrus')