Change `--since-commit` to `--commits`

[tarkatronic]

Feature Request

Is your feature request related to a problem? Please describe.

The current --since-commit option is not the most intuitive, and does not always work as expected.

Describe the solution you'd like

Instead of the current --since-commit, we should allow git-style refs/range of refs to be specified. This will make much more sense to common git users, and will be far more flexible.

A user could then specify:

• --commits asdf1234..HEAD which would be the same as --since-commit asdf1234
• --commits asdf1234..qwer0987 to inspect a distinct range of commits, which is net new functionality
• --commits HEAD~5..HEAD which would be the same as --max-depth=5

[connorjburton]

+1 to this, we were using --since-commit in 2.x in our Jenkins pipelines as Jenkins provided us the last successful commit to be built, so we were only scanning the commits that hadn't been successfully built before.

--commits would give us the same functionality.