Jsonexpr

* BUILTIN
* C convenience functions

* ability to call a function returned by an expression evaluation.
* ability to write to an array or object returned by an expression evaluation.
* ability to create new variable through GLOBAL.
* fix memory leak.

* free tokens upon free of head AST
* allow function to be created then called immediately

* remove debugging message
* test script

* token as type

* bugfix unsetting the last element of a map