Change the project URL to BitBucket rather than PyPI

Currently, the project metadata on PyPI doesn't provide an easy way to navigate to the BitBucket repo. This change replaces the current self-link back to PyPI with the appropriate link to BitBucket.

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branch : ncoghlan/setuppy-edited-online-with-bitbucket-1401023748153
open script files to be copied in the develop command in binary mode.
Added tag 3.8 for changeset 2fa97c06cc01
Bumped to 3.9 in preparation for next release.
Merged in ncoghlan/setuppy-edited-online-with-bitbucket-1401023748153 (pull request #54)

Change the project URL to BitBucket rather than PyPI
Remove excess whitespace

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extra : rebase_source : db1f9496cdda75a9467fcfb867b82108773b0443
Perform actual symlink detection; alternate approach to answer Pull Request #53.

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extra : rebase_source : a70141cd6472cd8e4024be4037bfd89e4adcb396
Merged in davidoff/setuptools (pull request #56)

Script files to be copied in the develop command should be open in binary mode. Fixes #210.
Update changelog
Bumped to 4.0 in preparation for next release.