Support latin1 strings with ascii target_url's

[twolfson]

We have encountered a regression when an ascii target_url attempts to use a latin1 string in its target URL. We should support proper coercion:

>>> resolve_link.resolve_link('twolfson', 'http://github.com/')
'http://github.com/twolfson'
>>> resolve_link.resolve_link(u'twolfsõn', 'http://github.com/')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "resolve_link/__init__.py", line 26, in resolve_link
    tmp_src_url = '//{src_url}'.format(src_url=src_url)
UnicodeEncodeError: 'ascii' codec can't encode character u'\xf5' in position 6: ordinal not in range(128)

[twolfson]

This has been fixed in #3 and released as 1.1.0.