Modify lval_print to print function names
	Modify lval_fun constructor to set sym field to function name
	Modify lval_copy to copy sym field for lval_fun
Modify lval_print to print functions as <function: function_name>
builtin_vars function for printing all symbols in environment
	Currently requires calling with an argument, change?
Modify lenv to track reserved symbols
	Modify lenv_new and lenv_del to init/cleanup reserved symbol list
	Add lenv_put_reserved function to add to reserved symbol list
	Add builtin_reserved function to print all reserved symbols