RFE: Generate changelogs for repos' releases that don't explicitly provide them

[TPS]

@vfeskov Most of the repos I've muted in G👊 because they don't actually provide usable changelogs when I'm notified, or @ least, for not every notified release. Many of those would be better served by printing the commit comments (which is what most changelogs do, anyway.)

Here's an example from a repo (that has no recent releases, but that's not really relevant here):
If 1 checks https://github.com/jsummers/tweakpng/releases, 1 would notice that there's no changelog given for any. However, if 1 looks @ the diff between the most current release & the previous @ jsummers/tweakpng@9e8ce2d...68deede, the full commit comments (if truncated, try the "…") are plenty. Is it possible to publish these via G👊?

Optionally, 1 might want only or additionally these generated changelogs, so those could be suboptions.

[TPS]

Here's an even better option, if a changelog is updated, but not transcluded, use it, e.g., https://github.com/bromite/bromite/releases. But remember to include only the diff of the changelog the same way, so as not to get all previous changes, also.

[TPS]

After reading changelog @ https://github.com/M66B/open-source-email/releases, I find that 1 can diff between version #s simply by inserting before & after ellipses, so for my example above, jsummers/tweakpng@1.4.5...1.4.6 works! Should make accomplishing this 💯× easier!

[TPS]

Maybe for those who really want lean e-mail notification, the reverse should also be available, i.e., just release version info, w/o any changelogs @ all.