SDCard destructor

I have no idea why it's taken so long for someone to point this out; but when the SDFile is destructed, it should always call close.

I hate to imagine how many people have been bit by this bug that just shouldn't exist.

The fact that it forces us to use the namespace and then typenames itself is pretty nasty; but understandable to make it easier for non-programmers...
The fact that it doesn't call close at the end is just one of the reasons why people end up hating C/C++.