Fluent interface for AST nodes

Branch: alexdura/jastadd2:fluent-interface
Branch: jastadd/jastadd2:master
Merged
Merged pull request
Fix template error from pull request 10
Description
Add a fluent interface to AST nodes
Modify the methods that add or update children of an AST node to return a reference to the AST node that is updates (i.e. this).