Add CLI for updating package version

Like 'npm version', but also updates sl-blip dep if present, doesn't
touch git, and doesn't fail if the version doesn't change.
slt-release: update sl-blip deps if present

Switch slt-release to use the version setting in strong-tools. It
doesn't treat an unchanged version as an error and it also updates
the sl-blip dependency if present.

This will help with strongloop-internal/scrum-nodeops#182

As a bonus, resolves #16
Use sl-blip
Ensure versions are properly formatted
slt-release: normalize version prefixes

If both vX.Y.Z and X.Y.Z should result in the same branch/tag names
and commit messages.