Fix typos and markdown (#2388)

* Fix typos

* Align properly

* Update core/consensus/slots/src/lib.rs

Co-Authored-By: cmichi <mich@elmueller.net>

* Update core/network/src/test/mod.rs

Co-Authored-By: cmichi <mich@elmueller.net>

* Update core/finality-grandpa/src/communication/mod.rs

Co-Authored-By: cmichi <mich@elmueller.net>

* Update core/consensus/common/src/import_queue.rs

Co-Authored-By: cmichi <mich@elmueller.net>

substrate/core/network-libp2p/src/custom_proto/handler.rs

@@ -194,7 +194,7 @@ enum ProtocolState<TMessage, TSubstream> {
 	},
 
 	/// We sometimes temporarily switch to this state during processing. If we are in this state
-	/// at the beginning of a method, that means something bad happend in the source code.
+	/// at the beginning of a method, that means something bad happened in the source code.
 	Poisoned,
 }