[maven-release-plugin] prepare release 4.2.1
[maven-release-plugin] prepare for next development iteration
Merge pull request #519 from sharwell/release/4.2.1

Release/4.2.1
Update CHANGES.txt
update for 4.2.1
add link to the releases
Merge remote-tracking branch 'antlr/master' into optimized
Fix incorrect condition in the full-context DFA support
Merge branch 'fix-full-ctx-dfa' into optimized
Add option TestPerformance.REPORT_SECOND_STAGE_RETRY
Implement hashCode, equals, and toString for Pair and Triple
Merge pull request #524 from sharwell/report-retry

Add option TestPerformance.REPORT_SECOND_STAGE_RETRY
Merge pull request #525 from sharwell/tuple-features

Implement hashCode, equals, and toString for Pair and Triple
Documented Grammar.defineRule, and updated it to return true if the rule was added to the Grammar
Added Grammar.undefineRule to support undefining rules prior to AST construction
Merge pull request #526 from sharwell/def-undef

defineRule and undefineRule
Merge remote-tracking branch 'antlr/master' into optimized
Implement toString for Tuple classes
Merge branch 'tuple-tostring' into optimized
When delaying error reporting because prediction escapes the decision entry rule, we should evaluate predicates to turn off any configurations that are invalid semantically. After that, we can collect the list of alternatives that are satisfied with the input thus far and then choose the minimum as before. Fixes #529