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/storage/generator.rs

@@ -53,7 +53,7 @@ pub use rstd::borrow::Borrow;
 #[doc(hidden)]
 pub use rstd::marker::PhantomData;
 
-pub use substrate_metadata::{
+pub use srml_metadata::{
 	DecodeDifferent, StorageMetadata, StorageFunctionMetadata,
 	StorageFunctionType, StorageFunctionModifier
 };