task 8: make customization of RuleFailedException easier

https://github.com/LorenzoBettini/xsemantics/issues/issue/8

Fixes #8

Change-Id: I3674ee512357ab98b1832a3c21c2a58fef59e04c
updated jacoco configuration note

Change-Id: I70cb08e8f89dc9ce90a488eb6fd0d6542c45c3b5