Support for richer patterns with var with names and function calls wi…

[AjayBrahmakshatriya]

…th arguments

This changeset just adds supports for richer patterns -

1. var can now have var_names as part of the pattern itself. This needs to match and will also be used in creation of new variables
2. function_call_expr can now have children and will be used for checking and creation,

Both of these are required for the tutorial