Categorise commits in merge collectively

[TTitcombe]

Is your feature request related to a problem? Please describe.
Sometimes (often) it takes several commits to make one complete feature change. as doculog currently works, this create false positive/duplicate features in the changelog. doculog should interpret

Describe the solution you'd like
A clear and concise description of what you want to happen.

Describe alternatives you've considered
None

Additional context
N/A