Import and use directives

Two new directives have been added to allow namespace functions to be used within the template. The use directive is for PHP use statements. The import directive accepts the namespace of the functions to import. It iterates through the list of user defined functions and creates a use function statement for each function for that namespace. An import configuration has been added to the compiler template so that the parser can automatically create the namespace use function statements to import for all templates.

The pointer for the compiler engine stack is now reset each time the engine called to compile a template.