Allow binding of text/blobs without SQLITE_TRANSIENT?

[jgallagher]

Currently, we always pass the SQLITE_TRANSIENT flag when binding a text or blob parameter, instructing SQLite to make its own copy of the data. It would be nice to be able to avoid that copy if we can come up with a safe interface that allows it. (Initially discussed on #162.)

[jgallagher]

If we merge #163, we'll know from the ToSqlOutput case if SQLITE_TRANSIENT is definitely required (if we get a ToSqlOutput::Owned, the value will be dropped immediately after it's bound). If we get a ToSqlOutput::Borrowed, it's conceivably safe to use SQLITE_STATIC if we can structure the API in such a way as to know the parameter(s) will still be alive when the query is executed.

[obsgolem]

Note that ToSqlOutput::Owned Strings and Boxs could conceivably be handled by passing in a deleter function pointer to Sqlite, thus allowing us to avoid a copy in the owned case as well.

[gwenn]

Vec::into_boxed_slice / String::into_boxed_str + Box::into_raw / drop(Box::from_raw)

[gwenn]

To be fixed here:

rusqlite/src/statement.rs

Lines 730 to 732 in 51a69b1

	ToSqlOutput::Borrowed(v) => v,
	ToSqlOutput::Owned(ref v) => ValueRef::from(v),