Support markdown/html output for describe/validate in CLI

[roll]

Overview

This is basically implemented within framework but not really exposed (although we already support frictionless describe --markdown

Specs

frictionless describe table.csv --html
frictionless validate table.csv --html
frictionless validate table.csv --markdown
frictionless convert schema.json --html

Plan

• [ ] implement metadata.to_html() -- should be as easy as platform.marko.convert(self.to_markdown())
• [ ] add html support to program.describe
• [ ] add markdown support to program.validate
• [ ] add markdown support to program.validate
• [ ] add html support to program.convert
• [ ] tests