setup.py: Use __url__ and __author__ from rss2email/__init__.py

Instead of duplicating those values locally.  This gives us one less
place to forget to update the next time we change the website or
maintainer.

Also, update __url__ to point to my GitHub repository and shift the
email address to rss2email.__email__.
error: Import __*__ metadata (URL, author, email)

These are used to format some of the log messages.