Allow for initial release mode

[kpdecker]

If the initial release number has been seeded (or incorrectly listed) in the package.json file, we should allow for a mode that ignores the missing tag and treats the operation as a new one.

Two options here:

1. Do this automatically and don't error, if there are no release notes files in the repo
2. Add an --iniital flag that the error can reference when in this state.

[jherr]

+1