Added feature: checkProperty

checkProperty has a random input generator and a property. It generates
inputs and throws a PropertyViolatedException if the property returns
false for any case. JUnit can pick up this exception and call the
whole test failed.
Exceptions in property are annotated with the input that caused them.
Added Filtering; Ignored target folder.
Added check if filters on generators are too strict.
Added javadoc for the functions.