Interface improvements

This release improves on the unseal subcommand by making the password command-line argument optional and prompting on stdin if it is not provided.

Handling for relative paths is fixed for both the seal/unseal commands by canonicalizing the input paths.

Generated password length is expanded to 6 words, which is the recommendation in RFC2289.

Release artifacts are compiled as fat binaries with libsodium statically linked! This means that libsodium no longer needs to be pre-installed on the platform! Just drop the binary in your $PATH and go!

Initial Release

Fix decoder tests and do rustfmt (#4)

* Update decoder tests to match new builder params

* rustfmt all of the things

* Provide more control over output location