Use SemVer RC versioning

[pagbabian-splunk]

We have used the 0.99.x format for our Release Candidate labeling. This proposal suggests we move to a SemVer convention found here: https://semver.org/spec/v2.0.0-rc.1.html

Our RC label would move from 0.99.2 to 1.0.0-rc.2.

Changes during the RC period would be rolled up with increments of the rc integer: e.g. rc.2, rc.3, etc.

A problem with the current scheme is that our rule is that improvements that are non-breaking are minor version, not patch version increments, hence the move we made from 0.99.1 to 0.99.2 did not conform to that rule, as we added session attributes.

Also, while the RC review period is not intended to a feature enhancement opportunity, it can be open to any and all proposals, including breaking changes if agreed upon before 1.x.x GA. Those potential changes would still be represented by the rc increment, keeping the 1.0.0 base version intact.