write detailed CHANGELOG.md test

[timziebart]

The current CHANGELOG.md test simply checks whether there has been any change at all, see

PowerDynBase.jl/.travis.yml

Line 47 in 55d7866

- git diff HEAD master --name-only | grep ^CHANGELOG.md$ || (ret=$? && echo -e "${RED}${BOLD}You didn't provide the details of your change in CHANGELOG.md" && exit $ret)

Suggestion: Write a test script (bash, Python, Julia) that checks for the following features:

• is the Version number given correctly, i.e. the uppermost subheadline should be ## Version a.b where (with the current version being x,y.z) either a==x+1 && b==0 or a==x && b==y+1 holds.
• are the badges inserted and match the Labels of the PR (bug/bugfix, enhancement)
• does the description match the PR subject
• does the link refer to the PR