Self-encryption

* Fix sodiumoxide to v0.0.10 as the new released v0.0.12 does not support rustc-serializable types anymore and breaks builds

* Use SHA256 instead of SHA512.

* Remove asynchronous code.
* Replace Deflate compression with Brotli.
* Use `Result`s instead of panic.

* Fix truncate, flagging first two chunks for encryption, and add new test.
* Updates contributor agreement.
* Fixed failing test exceeding serialisation limits.
* Disable clippy use_debug check.
* Updated dependencies.

* Updated dependencies.

* Various bug fixes and tidy up.
* Setup clippy usage.
* Include nightly builds on travis.