Support explicitly closing a connection

[jraymakers]

The explicit close method got removed when automatic memory management was added. But it can be useful to be able to explicitly close a connection.

A challenge is preventing the automatic memory management from double-freeing the connection after it is explicitly closed. To do this, we'll likely need to change the connection External to be a wrapper around the underlying connection pointer, so the underlying pointer can be cleared when it is explicitly freed.

[freakynit]

+1 for this.

When a developer knows for sure they don't need the connection anymore, allow them to close it.
Automated stuff is nice, but it shouldn't take away the explicit ability.

[recoye]

+1 for this.

[jraymakers]

This has been implemented in 1.1.3-alpha.8. Happy holidays! 🎉