Support encryption and decryption

[dhubler]

Add support for databag item encryption and decryption
https://docs.chef.io/data_bags/#encrypt
In chef, this happens in the client. Initial discussion started here
#101

I am looking to integrate https://github.com/bhoriuchi/go-chef-crypto and hopefully submit PR in next few days barring and setbacks

[MarkGibbons]

thanks!