Refactoring: change factory methods in AstBuilder to static
Implement Concats node
Merge remote-tracking branch 'upstream/master'
Merge remote-tracking branch 'upstream/master'
Add an Execute() to AstBuilder to run AST nodes
Generating AST for more nodes
Merge pull request #426 from ke-yu/master

Code refactoring for AstBuilder and generating AST for more nodes