[feature] need an easy way to decrypt and load encrypted settings file into memory

[kigster]

With gems such as railsconfig/config it would be nice to be able to simply load an encrypted file into memory.

The library should provide an easy way to auto-detect the private key, and have easy to use semantics for opening an encrypted file into memory.

For example:

require 'sym/file'
require 'config'

contents = Sym::File.new('production.yml.enc', key: 'MY_PRIVATE_KEY').read
Settings.add_source!(YAML.load(contents))

[kigster]

Addressed by the Sym::MagicFile API, and commit 7fe2834