Refactoring. Rename AstWalkerBase -> WalkerBase.
Merge remote-tracking branch 'origin/master'
Refactoring. Remove: IAstWriter, IAstReader, BinaryAstWriter, BinaryAstReader, AstKind.
Refactoring. Rename AstName -> ParseTreeName, AstModuleRelativeName -> ParseTreeName.
Refactoring. Remove RuleTypeTag enum.
Refactoring. SequenceInfo.Ast -> SequenceInfo.Root.
Refactoring. Rename AstSize -> RawSize.
Refactoring. SequenceCompileInfo.Ast -> SequenceCompileInfo.Root.