Consider replacing markdownlint by rumdl

[ruzickap]

Is your feature request related to a problem? Please describe.
Maybe it would be a good idea to replace markdownlint with rumdl.

Describe the solution you'd like
Adopt rumdl for faster linting and formatting with one binary. rumdl is markdownlint-compatible.

[nvuillam]

It could indeed be a good idea to add it and let users choose which one they want to use between markdownlint and rumdl :)

Would you like to submit a pull request ? :)