Dead code removed.
Work on recovery.
Add CanConsumeErrorTokens.
ParseToFailPos implemented.
Add Delete method to RecoveryParser.
Work on recovery. DeleteTokenOrGarbage implemented.
InsertSubrules implemented.
BuildAst implemented.
Merge remote-tracking branch 'GitHub/master' into RecoveryParserExperiment

Conflicts:
	Nitra.TestsLauncher/Recovery/Recovery.cs
	Nitra/Nitra.Runtime/Internal/Recovery/Recovery.cs
Work on recovery.
Work on recovery.
Work on recovery.
Add test.
Fix a bug in ErrorCollectorWalker.
False ambiguity fixed.
Fix ambiguous handler.
Fix astPtr check.
Refactoring.
Add IsAmbiguous property to Nitra.Ast.
Support for ambiguous Option, List and Sequence ast in PrettyPrint.