Metadata readble by others

[peppelinux]

Using nginx with some rewrite rules to publish metadata I got stucked on the default permissions created by pyff on newly created md files.

pyff creates default -rw------- permissions.

After tring to play with umask and setfacl I decided to handle this behaviour into the code.
See changes for a better view, if you agree we could put this as a configuration option.

All Submissions:

• Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• Have you added an explanation of what problem you are trying to solve with this PR?
• Have you added information on what your changes do and why you chose this as your solution?
• Have you written new tests for your changes?
• Does your submission pass tests?
• This project follows PEP8 style guide. Have you run your code against the 'flake8' linter?

[coveralls]

Coverage decreased (-0.04%) to 68.341% when pulling 402d289 on UniversitaDellaCalabria:metadata_readble_by_others into ab8246b on IdentityPython:master.