export: Display message about writing file

[msabramo]

This makes it consistent with Foreman (See #109) and is just nice for the user to know what is happening. Looks like this:

[marca@marca-mac2 export_test]$ honcho export supervisord .
[honcho export] writing: export_test.conf

[marca@marca-mac2 export_test]$ honcho export upstart .
[honcho export] writing: export_test-ansvc.conf
[honcho export] writing: export_test-ansvc-1.conf
[honcho export] writing: export_test.conf

[nickstenning]

This kind of output should go to sys.stderr I think.

[msabramo]

This kind of output should go to sys.stderr I think.

Done.

[nickstenning]

Ah, right, but I wouldn't use sys.stderr.write.

print(msg, file=sys.stderr)

[msabramo]

Updated.

[msabramo]

@nickstenning, @slafs: How does this look?

[slafs]

LGTM

[msabramo]

I should look at #119 before merging this

[nickstenning]

Added in 3d2b887.