Add some system for telling the developer to fix certain things in their emails

[Mange]

Roadie should have some form of reporting system where it can scan an email for bad patterns and tell the user about it.

Suggestions for "warnings":

1. Report on invalid URLs
2. Warn about <form>, etc. in the email

---

Reporting should be transparent and optional. Ideas on implementation:

• Test modules. Include them, run the assertions on the email.
  • This would be better served with another gem, right? roadie-doctor or something crazy like that..?
  • Doesn't help with detecting problems in production, where dynamic helpers might've ruined something that would appear okay in test.
• Callback for both enabling and for handling problems.
  • Makes it very optional. Sadly, also a bit of a threshold to climb to enable it.
  • See code sample 1 below.
• Store it on Document, when enabled.
  • Easier to enable and you can report it however you want afterwards. Might be more useful for more people since it's possible to send all of them in a single message.
  • See code sample 2 below.

# Sample 1
unless RACK_ENV == "production"
  document.report_problems = ->(error, doc) {
    My.logger.warn error
  }
end

# Sample 2
document.report_problems = true
html = document.transform
document.problems #=> [#<Roadie::Problem "Invalid URL: ...">]

[Mange]

This will probably not happen due to maintenance mode.

Maybe someone else wants to pick this up?