build_email_address() has always been a wrapper around Python's

formataddr(), which historically has taken a name and e-mail address

and built a resulting string in the form of name <email>. It handled

putting quotes around the name, if needed, and escaped certain

characters.
Python 3 extended the behavior to convert full names with Unicode values

into escaped =?=utf-8?...=?= strings. This is fine for formataddr(),

since it's there to create suitable header values, but it's not what we

wanted in this function.
This change rewrites build_email_address() to do its own e-mail

building. The logic is roughly the same as Python's implementation. The

meat of it is the usage of their regexes for escaping or quoting, which

we can still pull in fine.
Unit tests were added to check the results when using Unicode

characters, ensuring behavior remains consistent across Python versions.

Unit tests pass on Python 2 and 3.