Remove unused install_requires parameter in setup.py.

Also, renamed PyTest class to PyTestCommand and made
a couple cosmetic changes.
Merge pull request #913 from berkerpeksag/tweak-setup

Remove unused install_requires parameter in setup.py.
Simplify recursive-exclude rules in MANIFEST.in.
Merge pull request #916 from berkerpeksag/cleanup-manifest

Simplify recursive-exclude rules in MANIFEST.in.
Add selectors module to gunicorn codebase.

Closes #886.
remove option --debug and update documents
Merge pull request #918 from menghan/remove-deprecated

Remove deprecated option --debug, fix #917