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/executor/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[]
 //! Temporary crate for contracts implementations.
 //!
 //! This will be replaced with WASM contracts stored on-chain.
@@ -25,7 +24,6 @@
 //! - init_block(PrevBlock?) -> InProgressBlock
 //! - add_transaction(InProgressBlock) -> InProgressBlock
 //! It is left as is for now as it might be removed before this is ever done.
-// end::description[]
 
 #![warn(missing_docs)]
 #![recursion_limit="128"]