Automate release process

[romani]

Right now release process is a bit manual
https://github.com/checkstyle/sonar-checkstyle/wiki/How-to-make-release

I already did automation of github related steps:
https://github.com/checkstyle/eclipse-cs/blob/master/release.sh#L89
same will be done soon at main repo.

TODO: make same release.sh file sonar-checkstyle and gradually automate step by step from wiki page.
There was original idea at #53 to use special plugin, but I think now gihub api usage is best and most easy process.

[romani]

@muhlba91 , please help make release process more automated.