feat: Add 'Custom' sort_type to CommitGroup

[khos2ow]

What does this do / why do we need it?

This PR adds a new Custom sorting type to CommitGroup. This gives the ability to organize and order the sections based on their priority rather than alphabetically. For example Feature has logical precedence over Bug Fixes in list of changes.

How this PR fixes the problem?

Now there's a dedicated configuration for it:

options:
  commit_groups:
    sort_by: Custom <-- required keyword 
    title_order:    <-- predefined ordered list of titles to apply sort with 
      - feat
      - fix
      - enhance
      - refactor
      - perf
      - docs
    title_maps:
      docs: Documentation
      enhance: Enhancements
      feat: Features
      fix: Bug Fixes
      perf: Performance Improvements
      refactor: Code Refactoring

What should your reviewer look out for in this PR?

The reason for adding a []string{} to hold the order is because in go all the map's keys get sorted for predictability so technically there's no way to depend on that, so I added a new property (title_order) which is a slice and the order does in fact get preserved.

Check lists

• Test passed
• Coding style (indentation, etc)

Additional Comments (if any)

n/a

Which issue(s) does this PR fix?

fixes #60

[coveralls]

Pull Request Test Coverage Report for Build 156

• 26 of 26 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.09%) to 75.276%

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Totals
Change from base Build 155:	0.09%
Covered Lines:	1638
Relevant Lines:	2176

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💛 - Coveralls

[mavogel]

LGTM. Tested locally as I could not access the travis build

[khos2ow]

Yeah all these PRs are off of old travis which now seems to be in read-only mode to be migrated to travis-ci.com and we absolutely cannot do anything about them.

On top of that travis job on PRs are set to required and I couldn't merge one other PR. And I'm very curious how do you merge these now?

[mavogel]

Yeah all these PRs are off of old travis which now seems to be in read-only mode to be migrated to travis-ci.com and we absolutely cannot do anything about them.

I get rid of travis in #87 and unlink it in the repo. There was an active webhook.

And I'm very curious how do you merge these now?

I can overrule this with the admin priviledes.