Like many libsodium wrappers, and apparently *all* reasonable Rust bindings,
sodiumoxcide does not expose the `crypto_stream_xsalsa20_xor_ic` function,
necessary to use libsodium in an endless steam configuration.

https://nacl.cr.yp.to/stream.html
https://github.com/maidsafe/rust_sodium
https://groups.google.com/forum/#!original/boring-crypto/BpUmNMXKMYQ/EEwAIeQdjacJ