refactored out the logic to a seperate package to enable importing from other go programs
moved constructor function of SemverBumper to the top
renamend SemverBump.GetCurrentBumpedVersion() to GetCurrentVersion() to be more specific
removed unneeded pointers from SemverBumper.Init
Merge pull request #11 from giantswarm/library_refactoring

Refactored semver-bump to support usage as library