Move asserts in their own package; start to cleanup ParboiledTest

The ultimate goal is of course to get rid of it!
Start and write an assertion class for parsing results

Not quite there yet though.

But you have to start somewhere...
One more assert class, unused for now
Get rid of TestNgParboiledTest

We use TestNG anyway. No need for such an indirection.
Modify one parser example...

And learn something in the process; you can "inline" parsers within parsers.

Gives room for interesting possibilities...
One more "hand written test" replaced with an AssertJ assert
New assertion for a parse tree
Write assertions/tests for parse trees

Allows to replace String-based parse tree tests!

Getting there...
Rename NodeDescriptor to ParseTreeAssert
Minor code changes
ParseTreeAssert: use soft assertions
Rename ParseTreeAssert to ParseTreeVerifier
Modify assert code completely again
More tests, add errors

Basically I still have to rewrite a whole lot of stuff which is in the live
code.

But at least I can start and eliminate .toString() tests.
More testing: test return values now
More tests
Candidate verifier/assert class pair for statistics
Replace all deprecated usages in tests

This also means disabling one test.
A lot of code changes in there...

1. test the "no package" parser case;
2. move test parsers into their own specific package (except for the above);
3. start to rewrite ParserStatistics tests.
Start and test parser statistics based on JSON files