GH-42: UnicodeDecodeError - crashline w/ non-ASCII

Fixes: GH-42

Before:

```
❯ py.test _test_fail_unicode.py
Test session starts (platform: darwin, Python 2.7.6, pytest 2.6.4, pytest-sugar 0.3.5)
plugins: sugar


――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――― test ―――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――

    def test():
>       assert u'jello' == u'Bj\xf6rk Gu\xf0mundsd\xf3ttir'
E       assert 'jello' == 'Björk Guðmundsdóttir'
E         - jello
E         + Björk Guðmundsdóttir

_test_fail_unicode.py:4: AssertionError

   _test_fail_unicode.py ⨯                                                                                                                                  100% ▉▉▉▉▉▉▉▉▉▉▉

Results (0.01s):
   1 failed
Traceback (most recent call last):
  File "/Users/marca/python/virtualenvs/pytest-sugar/bin/py.test", line 9, in <module>
    load_entry_point('pytest==2.6.4', 'console_scripts', 'py.test')()
  File "/Users/marca/python/virtualenvs/pytest-sugar/lib/python2.7/site-packages/_pytest/config.py", line 41, in main
    return config.hook.pytest_cmdline_main(config=config)
  File "/Users/marca/python/virtualenvs/pytest-sugar/lib/python2.7/site-packages/_pytest/core.py", line 413, in __call__
    return self._docall(methods, kwargs)
  File "/Users/marca/python/virtualenvs/pytest-sugar/lib/python2.7/site-packages/_pytest/core.py", line 424, in _docall
    res = mc.execute()
  File "/Users/marca/python/virtualenvs/pytest-sugar/lib/python2.7/site-packages/_pytest/core.py", line 315, in execute
    res = method(**kwargs)
  File "/Users/marca/python/virtualenvs/pytest-sugar/lib/python2.7/site-packages/_pytest/main.py", line 116, in pytest_cmdline_main
    return wrap_session(config, _main)
  File "/Users/marca/python/virtualenvs/pytest-sugar/lib/python2.7/site-packages/_pytest/main.py", line 109, in wrap_session
    exitstatus=session.exitstatus)
  File "/Users/marca/python/virtualenvs/pytest-sugar/lib/python2.7/site-packages/_pytest/core.py", line 413, in __call__
    return self._docall(methods, kwargs)
  File "/Users/marca/python/virtualenvs/pytest-sugar/lib/python2.7/site-packages/_pytest/core.py", line 424, in _docall
    res = mc.execute()
  File "/Users/marca/python/virtualenvs/pytest-sugar/lib/python2.7/site-packages/_pytest/core.py", line 315, in execute
    res = method(**kwargs)
  File "/Users/marca/python/virtualenvs/pytest-sugar/lib/python2.7/site-packages/_pytest/terminal.py", line 360, in pytest_sessionfinish
    self.summary_stats()
  File "/Users/marca/dev/git-repos/pytest-sugar/pytest_sugar.py", line 314, in summary_stats
    self._getcrashline(report)
UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 86: ordinal not in range(128)
```

After:

```
❯ py.test _test_fail_unicode.py
Test session starts (platform: darwin, Python 2.7.6, pytest 2.6.4, pytest-sugar 0.3.5)
plugins: sugar


――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――― test ―――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――

    def test():
>       assert u'jello' == u'Bj\xf6rk Gu\xf0mundsd\xf3ttir'
E       assert 'jello' == 'Björk Guðmundsdóttir'
E         - jello
E         + Björk Guðmundsdóttir

_test_fail_unicode.py:4: AssertionError

   _test_fail_unicode.py ⨯                                                                                                                                  100% ▉▉▉▉▉▉▉▉▉▉▉

Results (0.02s):
   1 failed
      - /Users/marca/dev/git-repos/pytest-sugar/_test_fail_unicode.py:4: assert 'jello' == 'Björk Guðmundsdóttir'
```