Add commit_format option

[thislooksfun]

This adds the new option commit_format. It is either a string, in which case it resolves to one of the pre-defined patterns in SemanticReleaseHelper.format_patterns, or it can be passed a Regexp object, in which case that becomes the pattern through which the commit messages will be processed.

Examples:

lane :changelog_angular do
  analyze_commits(match: 'v*', commit_format: 'angular')
  notes = conventional_changelog
  puts(notes)
end

lane :changelog_custom do
  # will match commits of the form 'cl-<type>[.scope]= <subject>'
  analyze_commits(match: 'v*', commit_format: /^cl-(\w*)(?:\.(.*))?()= (.*)/)
  notes = conventional_changelog
  puts(notes)
end

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Notes:

• Since this change defaults to the previous value, it is backwards-compatible.
• This adds two built-in options:
  • default - the default previous behavior
  • angular - the angular format

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Closes #22

[xotahal]

Thanks for this @thislooksfun 🙏 Could you please resolve the conflict?

[thislooksfun]

@xotahal Conflict resolved!