Serve 2 version incrementors for stable and unstable releases

[askirmas]

Source semver/semver#559

Suite

current	command	next	incremented
v1.0.0	minor	1.1.0	1.0.0
v1.1.0	preminor pre-release	1.2.0-0	1.1.0
v1.2.0-0	patch	1.1.1	1.1.0
v1.1.1	preminor pre-release	1.2.0-1	1.2.0-0
v1.2.0-1	minor	1.2.0	1.2.0-1

Implementation idea

git tag --sort=-v:refname
| egrep "^v[0-9]+(\.[0-9]+){0,2}$"
| head -1
| gawk '{ match($0, /^v([0-9]+\.[0-9]+)\.([0-9]*)$/, arr)}{patch=arr[2]+1}{print arr[1]"."patch}'