Add release script

Release script automates release process:
 * bumps version in python version file
 * bumps version in debian changelog
 * add entry in debian changelog
 * commits release changes
 * add tag with proper release version name

Example of usage:

 ./scripts/release.sh minor "Rafal Wojdyla" ravwojdyla@gmail.com
 "Add release script"
Not sure if I like that a pretty small python project contains a sh-util library.