implemented basic scope_t structure including a unit-test
fixed memory-leaks in unit-test
implemented scope_equals()-function
fixed scope_equals()-function
implemented generic stack structure including a unit-test
implemented stack_get_top_item()-function and updated stack_t unit-test
integrated scope-stack into symbol-table, implemented unit-test for symtab_t
implemented function-scopes, using the symtab_enter_scope() and symtab_leave_scope() functions