Markdown linter (#1309)

* Add markdown linting

- add linter default rules
- adapt rules to current code
- fix the code for linting to pass
- add CI check

fix #1243

* Fix markdown for Substrate
* Fix tooling install
* Fix workflow
* Add documentation
* Remove trailing spaces
* Update .github/.markdownlint.yaml

Co-authored-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>
* Fix mangled markdown/lists
* Fix captalization issues on known words

substrate/frame/examples/split/README.md

@@ -3,7 +3,7 @@
 A simple example of a FRAME pallet demonstrating the ability to split sections across multiple
 files.
 
-Note that this is purely experimental at this point. 
+Note that this is purely experimental at this point.
 
 Run `cargo doc --package pallet-example-split --open` to view this pallet's documentation.