chore(common): history reporting fixes

1. Adds parsing of commit comments to extract PR title + number.
2. Uses `--first-parent` to exclude merges that are not to the
   base branch. This means that if you merge a PR into another, that
   child PR will not be listed in the history. From my perspective, this
   is fine -- we prefer chained PRs to be merged bottom-up rather than
   top-down, and this allows for PRs to be collapsed into one history
   entry if we really want that anyway.
3. Cleans up the git log range to work correctly regardless of your
   current branch.
4. Reads git log information from origin/base rather than base.

Note: this assumes that you have recently `git fetch origin` (or
`git pull origin`); that's up to you.