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/sr-sandbox/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[]
 //! This crate provides means to instantiate and execute wasm modules.
 //!
 //! It works even when the user of this library executes from
@@ -30,12 +29,10 @@
 //! When this crate is used in the `std` environment all these functions are implemented by directly
 //! calling the wasm VM.
 //!
-//! Example of possible use-cases for this library are the following:
+//! Examples of possible use-cases for this library are not limited to the following:
 //!
 //! - implementing smart-contract runtimes that use wasm for contract code
 //! - executing a wasm substrate runtime inside of a wasm parachain
-//! - etc
-// end::description[]
 
 #![warn(missing_docs)]
 #![cfg_attr(not(feature = "std"), no_std)]