Support for Conventional Commits

[kzantow]

What would you like to be added: Support for using Conventional Commits to generate feature, fix, and breaking/major version changes from commit or PR messages.

Why is this needed: Not all users will want to tag issues and PRs in specific ways and would like to rely on using Conventional Commits and similar strategies with commit descriptions to automate the aspects of version speculation and changelog generation.

Additional context: I believe with Conventional Commits, we have just a few basic things to check:

• fix: prefixed commits increment the patch version
• feat: prefixed commits increment the minor version
• commits which "appends a ! after the type/scope" or "has a footer BREAKING CHANGE:" increment the major version

Other commits don't necessarily contribute to version increments.