docs: Extends #999. Remove disused package readmes. Rename to sr-metadata. Fix Readme Rustdoc names (#1016)

* docs: Remove safe-mix since is no longer local dependency

* docs: Fix existing packages link. Still only includes Substrate Core

* docs: Remove empty package Readmes. Remove old docs links. Rename to Readme

* docs: Remove link to old docs

* misc: Merge latest from master. Renaem to sr-metadata. Fix list of RustDoc package names

* Rename substrate-metadata to sr-metadata, since it is in the "srml" subdirectory

* Change example to use package name that opens all packages in RustDocs

* Fix list of packages names that are available to open in RustDocs

* fix typo

* fix ordering of CLI options and add missing backslash

substrate/core/state-db/src/lib.rs

@@ -14,7 +14,6 @@
 // You should have received a copy of the GNU General Public License
 // along with Substrate.  If not, see <http://www.gnu.org/licenses/>.
 
-// tag::description[]
 //! State database maintenance. Handles canonicalization and pruning in the database. The input to
 //! this module is a `ChangeSet` which is basically a list of key-value pairs (trie nodes) that
 //! were added or deleted during block execution.
@@ -29,8 +28,6 @@
 //! # Pruning.
 //! See `RefWindow` for pruning algorithm details. `StateDb` prunes on each canonicalization until pruning
 //! constraints are satisfied.
-//!
-// end::description[]
 
 #[macro_use] extern crate log;
 #[macro_use] extern crate parity_codec_derive;