Validate config better

[marionebl]

commitlint is bound to become increasingly complex and already creates confusion for less common use cases. This is made worse by commitlint accepting unknown config keys:

• How to validate github issues / jira issues #237

Expected Behavior

• Throw when unknow config keys are encountered
• Be extra helpful when
  • a rule name is encountered in the root object
  • issuePrefixes is provided outside of parserPreset.parserOpts

Current Behavior

• Unknown config keys are accecpted without error

Possible Solution

• JSONSchema (compare webpack)

[armano2]

@escapedcat fixed as for #2412

[escapedcat]

Right, thanks @armano2 !