Fix windows bug in determining local timezone

[jjc385]

• New dependency -- tzlocal

Note that this also depends on my other pull request #9

See https://stackoverflow.com/a/16157307 for a discussion of pytz's issues getting the local timezone on Windows. The tzlocal package fixes the issue.

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Checks

• tzlocal.get_localzone returns a timezone object
• For me (on the east coast of the US), get_localzone() == timezone("America/New_York") is True