support unicode in log messages

[valentin-krasontovitsch]

When getting logs from a golang webserver
which reports response times in microseconds
I get the following error message

UnicodeEncodeError: 'ascii' codec can't encode character u'\xb5' in position 47: \
ordinal not in range(128)

Please add support for unicode - I personally think it should not be assumed that messaged will always be written in ascii. I will gladly submit a merge request if someone could guide me in the right direction.

Full stacktrace:

Traceback (most recent call last):
  File "/usr/local/bin/bonfire", line 11, in <module>
    load_entry_point('bonfire', 'console_scripts', 'bonfire')()
  File "/usr/local/lib/python2.7/dist-packages/click/core.py", line 722, in __call__
    return self.main(*args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/click/core.py", line 697, in main
    rv = self.invoke(ctx)
  File "/usr/local/lib/python2.7/dist-packages/click/core.py", line 895, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/usr/local/lib/python2.7/dist-packages/click/core.py", line 535, in invoke
    return callback(*args, **kwargs)
  File "/tmp/src/bonfire/bonfire/cli.py", line 200, in run
    run_logprint(gl_api, q, formatter, follow, interval, latency, output)
  File "/tmp/src/bonfire/bonfire/output.py", line 38, in run_logprint
    formatted_msgs = [formatter(m) for m in result.messages]
  File "/tmp/src/bonfire/bonfire/formats.py", line 75, in format
    return timestamp + ";" + ";".join(map(lambda f: "'{val}'".format(val=entry.message_dict.get(f, "")), fields))
  File "/tmp/src/bonfire/bonfire/formats.py", line 75, in <lambda>
    return timestamp + ";" + ";".join(map(lambda f: "'{val}'".format(val=entry.message_dict.get(f, "")), fields))
UnicodeEncodeError: 'ascii' codec can't encode character u'\xb5' in position 47: ordinal not in range(128)