Tag builds with SemVer pre-release versions and build metadata (closes #4, closes #5 and closes #6)

[mblomdahl]

How it works, assuming current release 1.2.1 and build number 5 according to Jenkins:

println(getBuildVersion('master', 5))
"1.2.1"

println(getBuildVersion('hotfix/1.2.0p1', 5))
"1.2.0p1-rc.5"

println(getBuildVersion('develop', 5))
"1.2.1+develop.dev5"

println(getBuildVersion('feature/I-want-a-sandwich-n0w', 5))
"1.2.1+feature.i.want.a.sandwich.n0w.dev5"

println(getBuildVersion('bugfix/issue-6', 5))
"1.2.1+bugfix.issue.6.dev5"

println(getBuildVersion('release/1.2.1', 5))
"1.2.1-rc.5"