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/srml/support/src/lib.rs

@@ -14,9 +14,7 @@
 // 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[]
 //! Support code for the runtime.
-// end::description[]
 
 #![cfg_attr(not(feature = "std"), no_std)]
 #![cfg_attr(not(feature = "std"), feature(alloc))]
@@ -29,7 +27,7 @@ pub extern crate sr_std as rstd;
 extern crate sr_io as runtime_io;
 #[doc(hidden)]
 pub extern crate sr_primitives as runtime_primitives;
-extern crate substrate_metadata;
+extern crate srml_metadata;
 
 extern crate mashup;