Support for 0.x semver mode

[coreyfarrell]

I have some a couple components that are currently on version 0.x.x (but never 0.0.x). I'd like to propose a flag to enable 0.x mode for version bumps. Right now I have to manually use standard-version -r minor for breaking changes, standard-version -r patch for non-breaking features. Bug fix releases already do the right thing.

To be clear, I want something like standard-version --version-zero, to block bumping to 1.0.0, shift the meaning of semver: 0.breaking.(feat|fix). npm allows a dependency on ^0.1.0 to install 0.1.1 but not 0.2.0, so ^0.1.0 should allow updating to any non-breaking release from 0.1.0.

[bcoe]

we should address this here: #310
I'm very much a proponent of this functionality, and think we should default to it with a breaking change in standard-verison.

[coreyfarrell]

@bcoe can we get a release of standard-version that uses conventional-changelog@3.1.9? If you're not ready to promote the [conventional-changelog/conventional-changelog}(https://github.com/conventional-changelog/conventional-changelog/) modules to latest maybe we could get a next release of standard-version to use those versions?