Ability to merge release back to develop

This preserves the correct version when merging a release back into develop.
This also changes the semantics of the 0+1 part of the semantic version so that it represents the number of changes since the previous tagged release (e.g. version 1.0.0-beta.1+5 gets reset to 1.0.0-beta.2+0)
Merge pull request #291 from dtabuenc/merge-release-back-to-develop

Ability to merge release back to develop