Review all FAIL and WARN messages, and provide fix suggestions

[davelab6]

Observed behaviour

WARN and FAIL results need a complete review by me or someone else who is a practicing type designer; as maintainer, @felipesanches has provided informative messages, but does not always have the full context of a type designer.

Expected behaviour

WARN and FAIL results should tell the user what to do to fix them; possibly including the name of the https://github.com/googlefonts/gftools script that can help.

Resources and exact process needed to replicate

This came up in the context of Orbitron VF today.

[felipesanches]

thanks, @davelab6!

[felipesanches]

@eliheuer this is exactly what we were discussing earlier this week.