Add commit rules

[Arthelon]

• Rules are going to be implemented as a list of rule configuration objects which contain the following fields
  • name (rule ID), valid boolean, check function
  • Check function takes the parsed commit message as an argument and might return an object like this: { valid: false, data: { ... } }
  • A CommitDiagnosis containing the check data is created for invalid commit diagnoses.
• Each rule's score is only added to the commit's overall score if the rule check is valid

[Arthelon]

List of default rules:

• subject-max-length (subject <= 50 characters)
• subject-min-length (subject >= 10 characters)
• subject-capitalize-first (capitalize first letter of the subject)
• subject-no-end-period (no period at the end of subject)