The textnonce dependency pulls in quite a few transitive dependencies.
However, we only use the dependency in a single location, to generate
MIME boundaries. For this, we can use `rand` directly (which is already
a transitive dependency anyways, since it's required by uuid).
This reduces the dependency count for a standard build from 117 to 105.
* Update dependencies (#386)
* Update dependencies and set MSRV to 1.40
* update hyperx
* Use display instead of description for errors
* Make hostname an optional feature
* Envelope from headers
* Update hyperx to 1.0
* rename builder to message
* Cleanup and make Transport send Messages
* Update rustls from 0.16 to 0.17
* Move transports into a common folder
* Merge imports from same crate
* Add message creation example to the site
* Hide "extern crate" in doc examples
* Add References and In-Reply-To methods
* Add message-id header
* Add blog posts and improve doc examples
