Option to suppress potential ERRORS to WARN

[smyrick]

As part of #136 we are talking about add this rule as a ERROR that you could opt-in to bring down to a WARN if you know what you are doing

Do we

• Have global list of errors to ignore
• Per location
• Argument
• Another directive
• Move to implementation details

[michaelstaib]

In the last working group we have decided that only warnings can be suppressed. All rules that produce warnings can either be promoted to produce an error or suppressed. An error is something that would lead to an invalid state.