Correction to null pointer in PogParamExpVisitor, fixes #303
Fix and test for bug #287
Added crude support for test result storage and comparison.
Clean up old test files.
Archive materials of old test framework
Test and fix (plus some support stuff) for #288
Fix and test for #291
Fix and test for #292
Fix and test for #293
Fix and test for #295
Update result file. State only added to POs if it exists now.
Tweak Playground for easier work with result files.
Added fix and test for #296
Test and fix for #299
updated test results po

this is mainly a list index change of the same result
updated string based po testing such that the following java property can be given to regenerate all tests:

-Dtests.po.override.all

or just

-Dtests.po.override.sl
-Dtests.po.override.pp
-Dtests.po.override.rt

note that results may change due to index changes in internal lists. This is safe to commit since it doesnt change the POs.
Record types for VDM-SL state should include an invariant, fixes #304
Fix problem with nil fields in sync clause expressions, fixes #302
Correct guards for static operations and variables
Correction to listener handling in value assignments