force utf8 mode when sys.stdout.encoding is ASCII

In some environments (particularly Docker), Python tends to start up
with the locale set to ASCII. That means trying to print unicode
characters raises an exception, like in our fancy display. Rather than
requiring the user to explicitly set PYTHONIOENCODING=utf8, we
rewrap stdout and stderr in UTF8 file objects.

I'm a little worried that this will break something down the line...

#136

peru/main.py

@@ -294,7 +294,22 @@ def docopt_parse_args(argv):
     'CommandParams', ['args', 'runtime', 'scope', 'imports'])
 
 
+def force_utf8_in_ascii_mode_hack():
+    '''In systems without a UTF8 locale configured, Python will default to
+    ASCII mode for stdout and stderr. This causes our fancy display to fail
+    with encoding errors. In particular, you run into this if you try to run
+    peru inside of Docker. This is a hack to force emitting UTF8 in that case.
+    Hopefully it doesn't break anything important.'''
+    if sys.stdout.encoding == 'ANSI_X3.4-1968':
+        sys.stdout = open(sys.stdout.fileno(), mode='w', encoding='utf8',
+                          buffering=1)
+        sys.stderr = open(sys.stderr.fileno(), mode='w', encoding='utf8',
+                          buffering=1)
+
+
 def main(*, argv=None, env=None, nocatch=False):
+    force_utf8_in_ascii_mode_hack()
+
     if argv is None:
         argv = sys.argv[1:]
     if env is None: