Export encrypted files to openssl compatible format

[langston-barrett]

I'd like to be able to export my files to an industry standard encrypted file format so that I can be sure that my data is safe and always retrievable.

If this issue is resolved, I'll post a bounty for automatic Dropbox sync.

Related to #149.

[langston-barrett]

I just posted a $10 bounty on this bug: https://www.bountysource.com/issues/40751368-export-encrypted-files-to-openssl-compatible-format