* Add module for blacklisting emails (self documented in sample config)

* Add module for blacklisting emails (self documented in sample config)
* Add command 'emails' for extracting emails from a message
* Rework protocol layout to allow expanding rspamd protocol by custom commands that can be added from anywhere in code
* Allow rspamc to work without strictly parameter 'command'. Command by default is 'symbols'.
* Update version to 0.1.8