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/keyring/src/ed25519.rs

@@ -79,7 +79,7 @@ impl Keyring {
 			.expect("static values are known good; qed")
 	}
 
-	/// Returns an interator over all test accounts.
+	/// Returns an iterator over all test accounts.
 	pub fn iter() -> impl Iterator<Item=Keyring> {
 		<Self as strum::IntoEnumIterator>::iter()
 	}