Using the notation data packets of signatures, we add a way to
set a context to detached signatures.
We also add a way to enforce that signatures have the right context
during verification.
* Refactor library, remove duplicates
* Rebuild structure to use Messages and Signature models
* Use PGPSplitMessage
* Remove signature model
* Various fixes
* Add helpers with tests
* Fixes, add some docs, add tests
* Add attachment helpers
* Add helpers Symmetric encryption
* Edit docs + examples
* Rename kr to keyRing
* Various fixes for documentation
* Edit JSON handling functions, add decrypt keyring via token
* Add proposal changes doc
* Fix CI
* Drop *Message functions, join CleartextMessage and BinaryMessage
* Change canonicalization and trimming only to text signatures
* Add cleartextsignature, detach signature from message model, move helpers
* Documentation, remove optional parameters
* Move verification to separate model
* Don't return message in VerifyDetached
* Update table of contents in readme
* Appease golint
* Run go fmt
* Rename Encrypt/DecryptMessageWithPassword to ..WithToken
These functions shouldn't be used with user-provided passwords,
as they don't do any key-stretching.
* Change key generation usernames
