Add git-semver next major, git-semver next minor and git-semver next patch functionality to the git-semver tool.
next major should increment the current major version by 1. It sets minor and patch version to 0.
next minor should increment the current minor version by 1. The major version is unmodified. It sets the patch version to 0.
next patch should increment the current patch version by 1. The major and minor versions are unmodified.
The result should be returned to the console. Tags will not be applied in the repo for this.