Unify printing

[mmastrac]

We have 6 different ways to print in the CLI. println/log/color_print support {} style parameters. print_markdown has its own placeholders and print is just strings.

• {e,}println
• echo!
• log::*
• print_markdown!
• print::
• color_print/cformat

Not currently counting the prompt and question APIs which also appear to be multiple...