Generating a salt for key derivation about js-encryptedfs

[CMCDragonkai]

Just remember that the details for how we did the AES GCM should be documented so it can be more easily verified.

[robert-cronin]

Here are some recommendations from NIST for GCM and GMAC. It is recommended to restrict the IV to a length of 96 bits (12 bytes) to support interoperability and some other factors.

Here is a good example of file encryption with AES-GCM and salt based key derivation in nodejs: https://gist.github.com/AndiDittrich/4629e7db04819244e843. I think this is a good example to follow. We are also missing the auth tag and cipher.final() from our implementation which are essential to adhering to the AES-GCM standard.

[robert-cronin]

this was solved in #23

[robert-cronin]

I have put some notes into the README along this line