Automated suggestions for semantic release number

[pinin4fjords]

Description of feature

Since we've started being clearer that we'd like folks to actually follow semantic versioning, and provided some more concrete guidance, it would be helpful if tools already provided some suggestions as to what a release should be.

e.g.:

• Changes to existing parameters since last release (definitely a major release)
• Additional parameters since last release, without changes to existing (maybe a minor version

Details very much up for grabs.