Improve email address parsing

* strip semicolons off both name and address
* single strip call for each
* lower case the email address for consistency

I've also put named variables in for name and address to make the code more
readable.

Finally I got rid of an inner for loop that appeared to yield the same result
repeatedly.  The loop was:

    for w in addr[0].split(" ") + [addr[1]]:
        yield addr

As w wasn't used in the loop, that will just yield the same value each time.
If this was meant to do something else, please say.
Allow duplicate names into database

By making sqlite not throw an error when the name is a duplicate.

Fixes issue #5
Merge pull request #11 from foobacca/clean_email

Improve email address parsing
Merge pull request #12 from foobacca/allow_duplicate_name

Allow duplicate names into database