CI: markdown link checker (#7145)

* change (CI): markdown link checker

* Fix some invalid doc links (re-run of cargo-unleash gen-readme w/ fixes).

* Fix some invalid doc links

* Fix some invalid doc links

* Fix some links

* Fix some links

* Apply @bkchr suggestions from code review

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

* Fix more links

* Fix more links

* typo

* Fix more links

* Fix more links

* Ignore valid link .. check wrongly sees it as invalid

* Fix style issue

* Fix style issue

* change (CI): update style guide link

* change (lib): suggestions

Co-authored-by: Dan Forbes <dan@danforbes.dev>
Co-authored-by: Steve Degosserie <steve@parity.io>
Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

substrate/client/chain-spec/README.md

@@ -4,7 +4,7 @@ This crate contains structs and utilities to declare
 a runtime-specific configuration file (a.k.a chain spec).
 
 Basic chain spec type containing all required parameters is
-[`ChainSpec`](https://docs.rs/sc-chain-spec/latest/sc_chain_spec/struct.ChainSpec.html). It can be extended with
+[`ChainSpec`](https://docs.rs/sc-chain-spec/latest/sc_chain_spec/struct.GenericChainSpec.html). It can be extended with
 additional options that contain configuration specific to your chain.
 Usually the extension is going to be an amalgamate of types exposed
 by Substrate core modules. To allow the core modules to retrieve

substrate/client/chain-spec/src/lib.rs

@@ -20,7 +20,7 @@
 //! a runtime-specific configuration file (a.k.a chain spec).
 //!
 //! Basic chain spec type containing all required parameters is
-//! [`ChainSpec`](./struct.ChainSpec.html). It can be extended with
+//! [`GenericChainSpec`]. It can be extended with
 //! additional options that contain configuration specific to your chain.
 //! Usually the extension is going to be an amalgamate of types exposed
 //! by Substrate core modules. To allow the core modules to retrieve