* Add support for rustls as TLS backend
* Use a "use-*" prefix for the TLS features
* Only enable rustls if native-tls is not enabled
* Allows several TLS components to coexist
* Update docs for rustls mentions
* Enable all features on docs.rs
* Rename TLS feature flags from "use-*" to "*-tls"
* Make native-tls the default
* Move TLS related errors to a separate enum
* Add changelog entry about rustls support
* Fix wrong naming in main error enum
* Simplify docs about tls feature flag usage
Alex Butler