Merge: + add --version command-line switch

Squashed commit of the following:

commit 631f5ddbeec8343462e5efd8e516ca489b7d5027
Author: Simon Zolin <s.zolin@adguard.com>
Date:   Fri Jan 10 15:20:53 2020 +0300

    --version

Configuration.md

@@ -32,6 +32,7 @@ Options:
   --check-config                     Check configuration and exit
   --no-check-update                  Don't check for updates
   -v, --verbose                      Enable verbose output
+  --version                          Show the version and exit
   --help                             Print this help
 ```