* fixed typo.
* fixed typo.
* delete the wrong template-specialized typedef.
* add the definition of type `maybe’.
* add the including header <memory>.
* [destructive change] the class `result_set’ renames `result_set_impl’.
* add the definition `self_type’.
* ctor and dtor are renamed.
* add the definition `result_set’.
* type `maybe_result_set’ was defined by wrapping up `result_set<T…>’ in `boost::optional<T>’. now, it is done by doing in `caprice::sqlitexx::maybe’.
* remove superfluous name mangling.
* add the definition type `maybe_compiled_statement’.
* add the definition type `maybe_statement’.